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handle this volume 

with care. 

The University of Connecticut 
Libraries, Storrs 

Wilbnr L. Cross Library 

University of Connecticut 


Tn Memory of 
Christie v7. Kason 





Anatomy and Physiology 




Qeajjuate op Bellevue Training School ; Assistant Sctpeuintkndent New York City 
Training School, Blackwell's Island, N. Y. ; formerly Assistant 


NeSu Hark 

All rights reserved 



Copyright, 1902, 

Set up and electrotyped September, 1894. Reprinted November, 1894; 
February, August, 1895; January, November, 1896; July, December, 
1897; September, 1898; July, 1899; February, October, 1900; March, 

New edition, revised, printed February, October, 1902; Febniarv, Oct. 
ober, 1903 • June, 1904; January, October, 1905 ; Januarj', 1906 ; January, 
October, 1907 ; January, July, 1908. 

^ffecttonatdg ©etitcateli 


%oum ©arcfje 





The following illustrations have been copied from Quain's 
"Anatomy" and Schiifer's "Essentials of Histology," and 
are used in this work by permission of the authors and pub- 
lishers of those books, viz. : Figs. 4, 5, 8, 10, 12, 14, 51, 53, 64, 
69, 83, 86, 103, 110, 117, 121, 127, 128. 


It is now seven years since the first edition of tliis " Text- 
book on Anatomy and Physiology for Nurses" was issued, and 
in order to bring the book up to date it has become necessary 
to revise it. 

That this revision has been accomplished with, I trust, success, 
is almost entirely owing to the kind assistance given me by 
Mr. T. Pickering Pick, and by Percy M. Dawson, M.D., 
Assistant Professor of Physiology in the Johns Hopkins Uni- 
versity, Baltimore. To the latter I am indebted for the whole 
recasting, and in large measure rewriting, of the chapter on the 
Nervous System, and also, to a slighter extent, of Chapters I. 
and XIX. Indeed, so greatly is this revision the work of 
Dr. Dawson that I should have been glad, had I been allowed, 
to place his name with mine on the title-page. 

The chapter on the Nervous System has been transferred 
to its usual position in such text-books, namely, following the 
chapter on Muscles, but it is, of course, possible for those who 
prefer the old arrangement to take this chapter later in the 
course of study. 

A number of new drawings have been made specially for 
this edition, including ten original ones by Dr. Dawson; also, 
to all the weights and measures, according to the English 
System, have been added their equivalents in the Metric 
System. It should be noted that the calculations are based 
upon the standard of weights and measures adopted by the 
United States, and not upon those of the British Pharmacopeia. 

November 12, 1901. 

D. C. K. 



(Lesson l.) 


Introductory — General Outline of the Body ; Structural Elements of the 

Body ; the Cell 1 


(Lesson 2.) 
Organs, Tissues, Cells ; Epithelial Tissues ; Stratified ; Transitional ; 

Simple 7 

(Lessons 3 and 4.) 
Connective Tissues : Connective Tissue Proper ; Adipose Tissue or Fat ; 

Cartilage ; Bone 13 


(Lessons 5, 6, and 7.) 

The Skeleton 23 


(Lesson 8.) 

The Joints 48 

(Lessons 9, 10, and 11.) 
Muscular Tissue : Striated or Striped ; Non-striated or Plain ; Attach- 
ment of Muscles to Skeleton ; Prominent Muscles of the Head and 
Trunk ; Prominent Muscles of the Limbs 53 

(Lessons 12, 13, and 14.) 
Nervous Tissue : the Neurone or Nerve-Cell ; Anatomy of the Nervous Sys- 
tem ; Physiology of the Nervous System ; Reflexes .... 74 

Note. — In most training schools in America instruction in class is given from 
October 1 to June 1, or for thirty-eight consecutive weeks; the lessons in this text- 
book can be conveniently mastered in the first year's course, taken in the manner 
indicated in these introductory contents. 




(Lesson 15.) 


The Vascular System : the Blood ........ 95 


(Lesson 16.) 

The Vascular System continued : Heart ; Arteries ; Veins ; Capillaries . 103 


(Lessons 17 and 18) 

The Vascular System continued : Arterial Distribution ; Venous Return . 115 


(Lesson 19.) 
The Vascular System continued : the General Circulation ; the Pulse and 

Arterial Pressure ; Variations in the Capillary Circulation . . . 131 


(Lessons 20 and 21.) 
The Vascular System concluded : Lymphatic Vessels and Lymph ; 

Lymphatic Glands and Bodies of Allied Structure .... 141 


(Lessons 22 and 23.) 
The Respiratory Apparatus : Larynx ; Trachea ; Lungs ; Respiration ; 
Effects of Respiration upon the Air within the Lungs ; upon the Air 
outside the Body ; upon the Blood ; Modified Respiratory Movements 151 


(Lessons 24 and 25.) 
Alimentation : Section 1. Preliminary Remarks on Secreting Glands and 
Mucous Membranes. Section 2. Food ; Food Principles ; Proteids, 
Fats, Carbo-hydrates, Water, Saline and Mineral Matters ; Chemical 
Composition of the Body ; Average Composition of Milk, Bread, and 
Meat ; Concluding Remarks 164 


(Lessons 26 and 27.) 
Alimentation continued : the Digestive Apparatus ; Alimentary Canal ; 

Accessory Organs 175 


(Lessons 28 and 29.) 
Alimentation concluded : Digestion ; Changes the Food undergoes in the 
Mouth, Stomach, Small and Large Intestines ; Summary of Digestion ; 
Absorption 191 



(Lessons 30 and 31.) 
Elimination : General Description of the Urinary Organs ; Structure and 


Blood-Supply of Kidneys ; Secretion of Urine ; Composition and Gen- 
eral Characters of Urine 201 


(Lessons 32 and 33.) 

Elimination concluded : the Skin ; Nails and Hair ; Bodily Heat ; Produc- 
tion of Heat ; Loss of Heat ; Distribution of Heat ; Regulation of 
Heat 212 


(Lessons 34, 35, and 36.) 

The Special Senses : Pressure, Temperature, Pain, Muscle-Sense, Taste, 

Hearing, Equilibrium, Vision 222 


(Lesson 37.) 
The Female Generative Organs . 243 

Glossary 253 

Index 273 



1. Diagrammatic Longitudinal Section of the Trunk and Head . . 2 

2. Diagram of a Cell 3 

3. Consecutive Stages of Cell-Division, with Indirect Division of the 

Nucleus 5 

4. Section of Stratified Epithelium 9 

5. Section of the Transitional Epithelium lining the Bladder ... 10 

6. Simple Pavement Epithelium 10 

7. Simple Columnar Epithelium 11 

8. Glandular Epithelium, with the Cells set round a Simple Saccular 

Gland 11 

9. Ciliated Epithelium from the Human Trachea 11 

10. Subcutaneous Areolar Tissue from a Young Rabbit .... 14 

11. Fibrous Tissue from the Longitudinal Section of a Tendon ... 15 

12. A Few Fat Cells from the Margin of a Fat Lobule . . . .17 

13. Articular Hyaline Cartilage from the Femur of an Ox . . . . 19 

14. Transverse Section of Compact Tissue (of Humerus) . . . .21 

15. The Skeleton 24 

16. The Clavicle 26 

17. The Scapula 26 

18. The Humerus 27 

19. The Ulna and Radius 28 

20. Bones of the Wrist and Hand ........ 29 

21. Os Innominatum ........... 30 

22. The Femur 31 

23. The Tibia and Fibula 32 

24. Bones of the Ankle and Foot 33 

25. Occipital Bone 34 

26. Parietal Bone 34 

27. Frontal Bone 35 

28. Temporal Bone ........... 35 

29. Sphenoid Bone 36 

30. Ethmoid Bone 36 

31. Nasal Bone 37 

32. Lachi-ymal Bone . 37 

33. Vomer 37 

34. Malar Bone 38 

35. Palate Bone 38 

36. Inferior Turbinated Bone 38 

37. Superior Maxillary Bone . 38 

38. Inferior Maxillary Bone 39 




39. Hyoid Bone 39 

40. A Cervical Vertebra 40 

41. Side View of Spinal Column, without Sacrum and Coccyx ... 41 

42. Thorax 42 

43. Sternum 43 

44. The Skull 44 

45. The Skull at Birth 45 

46. Male Pelvis 46 

47. Female Pelvis 46 

48. A Toothed or Dentated Suture 48 

49. A Mixed Articulation 48 

50. A Simple Complete Joint 49 

51. Muscular Fibre 53 

52. Fragments of Striped Fibres showing a Cleavage in Opposite Directions 54 

53. Wave of Contraction passing over a Muscular Fibre of Dytiscus . . 55 

54. Fibre-Cells of Plain Muscular Tissue 56 

55. Muscles of Right Eyeball within the Orbit 60 

56. Muscles of Eyeball 60 

57. Muscles of the Tongue 61 

58. Muscles of the Arm 67 

59. Muscles in Front of Forearm 68 

60. Muscles of the Thigh 70 

61. Muscles of the Leg. Superficial View of the Calf .... 70 

62. Nerve ending in Muscular Fibre of a Lizard 71 

63. Diagram of a Neurone 74 

64. Diagram illustrating the Arrangement of the Cerebro-Spinal System . 76 

65. Nerve-Fibres . . * 77 

66. Section of the Internal Saphenous Nerve 78 

67. General View of the Sympathetic System 79 

68. Diagram showing the Relation of the Cerebro-Spinal to the Sympa- 

thetic Neurones ........... 80 

69. Base of Brain, Spinal Cord, and Spinal Nerves 81 

70. Transverse Sections of the Spinal Cord at Different Levels ... 82 

71. Diagram showing Anatomy of the Spinal Nerve Roots and Adjacent 

Parts 83 

72. Diagram showing Relation of Neurones composing the Spinal Nerve- 

Roots with Adjacent Nervous Structures 84 

73. The Base of the Brain 86 

74. Reflex Arc 91 

75. Reflex Arc as it is approximately in Man 91 

76. Diagram of Nervous System 93 

77. Red and White Corpuscles of the Blood 97 

78. The Heart and Lungs 104 

79. Anterior View of Heart, dissected after Long Boiling, to show the 

Superficial Muscular Fibres 105 

80. Diagram of Heart and Pericardium 106 

81. Right Side of Heart 106 

82. Left Side of Heart 107 

83. Diagram to illustrate the Action of the Heart 108 



84. Section of Heart at Level of Valves 109 

85. Structure of an Artery Ill 

86. Part of a Vein laid Open 112 

87. Portion of Endothelium of Peritoneum 114 

88 and 89. The Aorta 117 

90. The Carotid, Subclavian, and Axillary Arteries 118 

91. Deep Anterior View of the Arteries of the Arm, Porearm, and Hand 119 

92. Iliac and Femoral Arteries 122 

93. View of Popliteal Artery 123 

94. Deep View of the Arteries of the Back of the Leg .... 124 

95. Anterior View of Arteries of the Leg 124 

96. Arteries of the Foot 125 

97. Sketch of the Principal Venous Trunks 126 

98. Superficial Veins of Lower Extremity 127 

99. Diagram of Circulation 132 

100. Isolated Capillary Network formed by the Junction of Several Hol- 

lowed-out Cells, and containing Coloured Blood Corpuscles in a 

Clear Fluid 140 

101. A Small Portion of a Lymphatic Plexus 142 

102. Lymphatics and Lymphatic Glands of Axilla and Arm . . . 146 

103. Diagrammatic Section of Lymphatic Gland 147 

104. Vertical Section of a Portion of a Peyer's Patch, with Lacteal Vessels 

Injected 148 

105. The Mouth, Nose, and Pharynx, with the Commencement of Gullet 

and Larynx 152 

106. The Larynx as seen by Means of the Laryngoscope . . . .153 

107. Front View of Cartilages of Larynx 154 

108. Two Alveoli of the Lung 155 

109. Anterior View of Lungs and Heart 156 

110. Diagram showing the Various Forms of Secreting Glands . . . 165 

111. An Intestinal Villus 169 

112. The Salivary Glands 177 

113. The Mouth, Nose, and Pharynx, with the Larynx and Commence- 

ment of Gullet, seen in Section . . . . . . .179 

114. Vertical and Longitudinal Section of Stomach and Duodenum . . 181 

115. An Intestinal Villus 182 

116. Section through the Lymphoid Tissue of a Solitary Gland . . . 183 

117. Csecum, showing its Appendix, Entrance of Ilium, and Ileo-csecal 

Valve 184 

118. Posterior View of Pancreas 186 

119. Under Surface of Liver 187 

120. Diagrammatic Representation of Two Hepatic Lobules . . .188 

121. Section of Eabbit's Liver, Vessels and Bile Ducts injected . . . 189 

122. The Renal Organs viewed from Behind 203 

123. Section through the Kidney 205 

124. Vascular Supply of Kidney 206 

125. Plan of Blood- Vessels connected with the Tubules .... 207 

126. Diagram of the Course of Two Uriniferous Tubules .... 208 

127. Section of Epidermis 212 


via. PAGE 

128. Section of Skin showing Two Papillse and Deeper Layers of Epidermis 214 

129. Piece of Human Hair 215 

130. Section of Skin showing the Hairs and Sebaceous Glands . . . 216 

131. Coiled End of a Sweat-Gland 217 

132. The Upper Surface of the Tongue 225 

133. Vertical Longitudinal Section of Nasal Cavity 227 

134. Semi-diagrammatic Section through the Right Ear .... 229 

135. Diagram showing Relative Position of the Planes in which the Semi- 

circular Canals lie 232 

136. The Left Eyeball in Horizontal Section from Before Back . . 234 

137. Diagram showing Relations of the Neurones and Sensory Epithelium 

in the Retina 236 

138. Diagram illustrating Rays of Light converging in (A) a Normal Eye, 

(B) a Myopic Eye, and (C) Hypermetropic Eye .... 239 

139. The Lachrymal Apparatus 241 

140. Section of Female Pelvis showing Relative Portion of Viscera . . 244 

141. The Uterus and its Appendages 246 

142. Section of an Ovary 248 



I, Forms of Muscles and Tendons 57 

II. Muscles of Face, Head, and Neck 59 

IIL Muscles of Back 63 

IV. Muscles of Chest and Abdomen 65 

V. The Abdominal Aorta and its Contents 121 

VI. Plan of Foetal Circulation 139 

VII. Regions of the Abdomen and their Contents 176 







Introductory. — In looking upon the fully developed human 
body we are impressed with the complexity of its structure, the 
perfection of its mechanism, the mysteriousness of its life. To 
learn to understand something of this structure, this mechan- 
ism, this life, is one of our most imperative duties as nurses; for 
how can we appreciate the significance of abnormal functions, 
and the seriousness of diseased conditions, unless we are ac- 
quainted with the normal functions of the body, and have some 
knowledge of healthy bodily conditions ? 

In the following pages we propose to give a description of 
the structure, of the position, and of the special work or func- 
tion of each part of the body. We have dwelt specially upon 
the structure of the different parts, believing that any correct 
understanding of the bodily functions must be preceded by a 
certain amount of knowledge concerning the structure of the 
organs performing these functions. 

Before taking up the subject in detail it is well, first of all, 
to get a general idea of the main divisions, and the position of 
the different parts, and we shall therefore begin our considera- 
tion of the body with an outline of its structure. 

Generg,l outline of the body. — It is readily seen that the human 
body is separable into trunk, head, and limbs ; the trunk and 
head are cavities, and contain the internal organs or viscera, 

B 1 


[Chap. I. 

while the limbs are solid, contain no viscera, and are merely 
appendages of the trunk. The limbs or extremities, upper 
and lower, are in pairs, and bear a rough resemblance to 
one another, the shape of the bones, and the disposition of 
the muscles in the thigh and arm, leg and forearm, ankle and 
wrist, foot and hand, being very similar. 

The trunk and head contain two main cavities, and looking 
at the body from the outside we should naturally imagine that 
these two cavities were the cavity of the 
head and the cavit}^ of the trunk, respec- 
tively. If, however, we divide the trunk 
and head lengthwise into two halves, by 
cutting them through the middle line 
from before backwards, we find the trunk 
and head are divided by the bones of the 
spine into back and front cavities, and 
not into upper and lower {vide diagram). 
The dorsal or back cavity is a com- 
plete bony cavity, and is formed by the 
vertebrae (bones of the spine) and by the 
bones of the skull. It may be subdi- 
vided into the spinal canal, containing 
the spinal cord, and into the cranial cav- 
ity, which is merely an enlargement of 
the spinal canal, and contains the brain. 
The ventral or front cavity is not a 
Fig. 1.- Diagrammatic complete bony cavity, part of its walls 
Longitudinal Section of being formed of muscular and other tis- 

THE Trunk AND Head. 1,1, ^ . 

the dorsal cavity; a, the suc ; it IS much larger than the dorsal 
spinal portion ; 6, the era- cavity, and may be subdivided into the 

nial enlargement; c, c, the '' *^ 

bodies of the vertebrae form- thoracic, abdominal, and pelvic cavities. 

ing the partition between rr^i .-i • •■ i , i • j.i 

the dorsal and ventral cavi- ^^^^ thoracic cavity, or chest, contains the 
ties ; 2, 2, the ventral cavity, trachea or windpipe, the lungs, gullet, 

subdivided into thoracic cav- , , i ,i , ^ ■ • 

ity (rf), abdominal cavity heart, and the great vessels springing 
(e), and pelvic cavity (/) ; from ^nd entering into, the heart. The 

g, the nasal cavity ; h, the . 

mouth, or buccal cavity, abdominal cavity contains the stomach, 
The alimentary canal (ao is j^ gall-bladder, pancreas, spleen, kid- 

represented running through " •■■ _ •■■ 

the whole length of the ven- neys, small and large intestines, etc. The 
ra cavi y. pelvic cavity contains the bladder, rec- 

tum, and in the female, the generative organs. Connected with 

— n 

Chap. I.] THE CELL. 3 

the upper part of the ventral cavity are two small cavities, the 
buccal cavity, or mouth, containing the tongue, teeth, salivary 
glands, etc., and the nasal cavity, containing the organ of smell. 

Structural elements of the body. — When any part of the body 
is separated by the aid of the microscope into its simplest parts, 
such parts are called its structural elements. The structural 
element of every part of the body is the cell. All the varied 
activities of the body are the result of the activity of the cells 
which compose it, and it is very desirable, owing also to their 
being the foundation of all structure (the bricks, as it were, 
out of which the tissues are built), that we early acquire some 
definite conception of these tiny elementary bodies. 

The cell. — A cell is a minute portion of living substance 
(protoplasm) which is sometimes enclosed in a membrane (cell 
membrane). It consists of a semi-fluid, 
often granular, part (cytoplasm) sur- 
rounding a more solid part (the nu- 
cleus). The nucleus differs somewhat 
from the cytoplasm in function and in 
chemical composition. Yryf A { Y F F^ c 

The study of physics shows us that 

all matter, of whatever kind it may be, -n. ^ t^ 

' J ■> Fig. 2. — Diagram of a 

is made up of little particles, or mole- Cell, n, nucleus; c, cyto- 
cules, so small that they are perfectly ^ ^^™' 
invisible to the human eye, even when aided by the most power- 
ful microscope ; and it is only when a great number of these 
molecules are collected together that they become perceptible. 
Again, a study of the chemical properties of matter teaches us 
that these molecules are in turn composed of still smaller parti- 
cles called atoms. There are only about seventy different kinds 
of atoms, whereas the different sorts of molecules which are 
formed by combination of atoms are innumerable. The prop- 
erty of atoms of uniting together to form molecules is known 
as their chemical affinity, while that which binds the molecules 
together is called cohesion.^ The strength of chemical affinity 

1 As examples of atoms and molecules we may mention the following : 
hydrogen (H) and oxygen (0) unite by chemical affinity to form the hydro- 
gen monoxide (H2O), or water molecule. Such molecules, when gathered 
together in great numbers and united by their property of cohesion, form 
the water which we can perceive by our senses. So also sodium (Na) and 
chlorine (CI) unite to form sodium chloride (NaCl), or common table salt. 


varies greatly, and hence in some substances the molecules can 
only with great difficulty be broken up into their component 
atoms. Such substances are said to be "stable." On the 
other hand, many substances are very easily decomposed, and 
are known as " unstable " substances. Between these two 
extremes there are substances possessing every degree of 

In protoplasm, or proteid (proteid being the name usually 
employed by chemists), the molecule is composed of carbon, 
hydrogen, nitrogen, oxygen, and sulphur, and is a highly com- 
plex structure. It is also extremely unstable, and is very 
sensitive to outside influences. The many vital phenomena 
exhibited by protoplasm are due, in great part, to the chemi- 
cal reactions of the atoms composing its molecules, and which 
are rendered possible by the great instability of these mole- 

During the life of a cell its protoplasm is constantly under- 
going changes, the chief of which may be enumerated as 
follows : — 

(1) All protoplasm coming in contact with oxygen absorbs 
it and combines with it. Whenever this combination takes 
place, a certain amount of the protoplasm is burned or oxi- 
dized, and as a result of this oxidation heat and other kinds of 
energy are produced, and carbon dioxide evolved. 

(2) All protoplasm is able to take to itself, and eventually 
convert into its own substance, certain materials (foods) that 
are non-living; in this way the protoplasm may increase in 
amount, or in other words the cell may grow. But if the 
amount of protoplasm does not permanently increase, this is 
due to the fact that just as much protoplasm is being broken 
down by the process of oxidation, and removed from the cell, 
as is added by the process of assimilation. Chemical changes 
which involve the building up of living material within the 
cell have received the general name of anabolic changes, or 
anabolism ; those, on the other hand, which involve the break- 
ing down of such material into other and simpler products, 
are known as katabolic changes, or katabolism ; while the sum 
of all the ana- and katabolic changes which are proceeding 
within the cell are spoken of as the metabolism of a cell. 
These chemical clianges are always more marked as the activ- 

Chap. I.] 


ity of the cell is promoted by warmth, electrical or other 
stimulation, the action of certain drugs, etc. 

(3) The most obvious physical changes that can sometimes 
be seen in living protoplasm, by the aid of the microscope, 
are those which are termed "amoeboid." This term is derived 
from the amoeba, a single- 
celled organism which has 
long been observed to exhibit 
spontaneous changes of form, 
accompanied by a flowing of 
its soft semi-fluid substance. 
By virtue of this property, 
the cells can move from one 
place to another. If one of 
these cells be observed under 
a high power of the micro- 
scope, it will be seen gradu- 
ally to protrude a portion of 
its protoplasm ; this protru- 
sion extends itself, and the 
main part or body of the cell 
passes by degrees into the 
elougated protrusion. By a 
repetition of this process, the 
cell may glide slowly away 
from its original situation and 
move bodily along the field 
of the microscope, so that an 
actual locomotion takes place. 
When the surface of these 
free cells comes in contact Fig. 3. — .4 to i7, Consecutive Stages 
with any foreign particles, the «*' Cell-Division, with indirect Divi- 

•^ . . SIGN OF THE NUCLEUS. (Diagrammatic.) 

protoplasm, by virtue of its 

amoeboid movements, tends to flow round and enwrap the 
particles, and particles thus enwrapped or incepted may then 
be conveyed by the cell from one place to another. 

The nucleus. — The nucleus of a cell is directly concerned in 
the nutrition and in the reproduction or division of the cells. 
In dividing, the nucleus passes through a series of remarkable 
changes, which are too complicated to be studied here. (See 


Fig. 3.) The result of these changes is that either directly 
or indirectly the nucleus splits into two, and the protoplasm 
divides and arranges itself around the new nuclei ; these 
daughter cells soon grow to the size of the parent cell, and 
division of these and consequent multiplication may proceed 
with great rapidity. 

To sum up : The cell assimilates, is continually building 
itself up and replenishing its store of energy, is as continually 
breaking down into simpler products with a setting free of 
energy; it grows; it moves; it reproduces itself — in other 
words, it is alive and is the basis of all life. 



Organs, tissues, and cells. — In speaking of the different parts 
of the body, we usually call each part an organ, and we may say 
that the human body is made up of organs, each organ being 
adapted to the performance of some special work or function. 
Thus the lungs are organs specially adapted for performing 
the function of respiration, the bones are organs adapted for 
support and locomotion, the kidneys for secreting urine, etc. 

Every part or organ, when examined microscopically, is found 
to consist of certain textures or tissues. When the body is 
thus analyzed by the aid of the microscope, we find that the 
number of distinct tissues is comparatively small, and some of 
these again, although at first sight apparently distinct, yet have 
so much in common in their structure and origin one with 
another, that the number becomes still further reduced, until 
we can only distinguish four distinct tissues, viz. : — 

The epithelial tissues. The muscular tissues. 

The connective tissues. The nervous tissues. 

Particles met with in the fluids of the body, such as the little bodies or cor- 
puscles in the blood and lymph, are also reckoned among these elementary 

Some organs are formed of a combination of several of the 
above tissues ; others contain only one or two. Thus the 
muscles are made up almost entirely of muscular tissue with 
only a small intermixture of connective tissue, blood-vessels, 
and nerves ; whilst the ligaments or sinews are composed 
wholly of a variety of connective tissue. 

On the other hand, there are certain organs or parts of the 



body not in themselves distinguished by the preponderance of 
any tissue. Such are : — 

Blood-vessels. Synovial membranes. 

Lymphatic vessels. Mucous membranes. 

Lymphatic glands and bodies Secreting glands. 

of like structure. Integument or skin. 
Serous membranes. 

Thus, though we may say the greater bulk of the body is made 
up of a combination of four distinct tissues, — the epithelial, 
connective, muscular, and nervous, — there are parts in which 
these tissues are so intimately mixed that we cannot distinguish 
any distinct variety, and we are therefore obliged to class them 
by themselves. 

As the structure of an organ depends upon the properties of 
the tissues composing it, so the characteristics of each tissue 
depend upon their ultimate structural units — the cells and the 
products of the cells. ^ 

The early embryo is an agglomeration of cells, and the whole 
of the body is developed out of one cell, called the ovum, 
which measures 2^0 ^^ 120 ^^ ^^ ^'^^^ (0.106 to 0.211 mm.) 
in diameter. In the beginning of the formation of the body, 
the protoplasm of the ovum divides and subdivides, and the 
daughter cells thus formed eventually arrange themselves in 
three la3'ers. These layers are known respectively as the epi- 
blast, or upper layer ; the mesoblast, or middle layer ; the hypo- 
blast^ or under layer. The epiblast is supposed to give rise to the 
nervous tissue and most of the epithelial tissue ; the mesoblast 
to the connective and muscular tissues, and also to a portion of the 
epithelial tissue; the hypoblast to the rest of the epithelial tissue. 
Of these tissues, the epithelial is the simplest and most nearly 
allied to the primitive tissue, and will first engage our attention. 

Epithelial tissue. — Epithelial tissue is composed entirely of 
cells united together by adhesive matter. The cells are gener- 
ally so arranged as to form a skin or membrane, covering the 
external surfaces, and lining the internal parts of the body. 
This membrane is seen when the skin is blistered, the thin and 
nearly transparent membrane raised from the surface being 

^ By the products of the cells is meant, for example, the fibres of connective 
tissue, or the intercellular substance of cai-tilage and bone. 


epithelial tissue — in this situation called epidermis, because it 
lies upon the surface of the true skin. In other situations, 
epithelial tissue usually receives the general name of epithelium. 

Classification. — We may classify the varieties of epithelium 
according to the shape of the cells which compose them, or 
according to the arrangement of these cells in layers. Adopt- 
ing the latter and simpler classification, we distinguish three 
main varieties : the stratified, consisting of many layers ; the 
transitional, consisting of two or three layers ; the simple, con- 
sisting of a single layer of cells. 

1. Stratified epithelium. — The cells composing the different 
layers of stratified epithelium differ in shape. As a rule, the 

Fig. 4. — Section of Stratified Epithelium, c, lowermost columnar cells; P, 
polygonal cells above these; fl. flattened cells near the surface. Between the cells 
are seen intercellular channels, bridged over by processes which j^ass from cell to cell. 

cells of the deepest layer are columnar in shape ; the next, 
rounded or many-sided, whilst those nearest the surface are 
always flattened and scale-like, the protoplasm of the cell being 
finally converted into a horn-like substance. The deeper soft 
cells of a stratified epithelium are continually multiplying by 
cell-division, and as the new cells which are thus produced 
in the deeper parts increase in size, they compress and push 
outwards those previously formed. In this way cells which 
were at first deeply seated are gradually shifted outwards and 
upwards, growing harder as they approach the surface. The 
older superficial cells are being continually rubbed off as the 
new ones continually rise up to supply their places. 

Stratified epithelium covers the anterior surface of the eye, 
lines the mouth, the chief part of the pharynx, the gullet, the 
vagina, and the neck of the uterus, but its most extensive distri- 
bution is over the surface of the skin, where it forms the epider- 
mis. Whenever a surface is exposed to friction we find stratified 



[Chap. IL 

scaly epithelium, and we may therefore classify it as a protec- 
tive epithelium. 

2. Transitional epithelium. — This is a modification of strati- 
fied epithelium, consisting only of two or three layers of cells. 


(Highly magnified.) (E. A. S.) «, superficial; 6, iutermediate; c, deep layer of cells. 

The superficial cells are large and flattened, having on their 
under surface depressions into which fit the larger ends of the 
pear-shaped cells which form the next layer. Between the 
tapering ends of these pear-shaped cells are one or two layers 
of smaller, many-sided cells, the epithelium being renewed by 
division of these deeper cells. This kind of transitional epithe- 
lium lines the bladder and ureters. 

3. Simple epithelium. — This is composed of a single layer of 
cells. The cells forming single layers are of distinctive shape, 
and have distinctive functions in different parts of the body. 
3 The chief varieties are the pavement, col- 
umnar, glandular, and ciliated. 

In simple pavement epithelium the cells 
form flat, many-sided plates or scales, which 
fit together like the tiles of a mosaic pave- 
ment. It forms very smooth surfaces, and 
' lines the alveoli of the lungs, the heart, 
from a serous membrane; blood-vcssels, and lymphatics; the mam- 

6, from a blood-vessel. i , ,i •.• . 

mary ducts, the serous cavities, etc. 
The columnar epithelium is a variety of simple epithelium in 
which the cells have a prismatic shape, and are set upright on 
the surface which they cover. In profile these cells look some- 
what like a close palisade, their edges, however, being often 
irregular and jagged, especially where free or " wander-cells " 

Fig. <i. — SiMPLK Pave 
MENT Epithelium. a 

Chap. II.] 



Fig. 7. — Simple Col- 
umnar Epithelium, a. 

squeeze in between them. Columnar epithelium is found in its 
most characteristic form lining the mucous 
membrane of the intestinal canal. 

Glandular epithelium is found in the re- 
cesses of secreting glands. The cells are of 
many different shapes, and are usually set 
round a tubular or saccular cavity, into the cells; 6, intercellular 

1 • 1 .-i , • • 1 rpi , substance between the 

which the secretion is poured. The proto- i^^^er end of cells, 
plasm 01 these cells is generally filled by 

the materials which the gland 


In ciliated epithelium the cells, 
which are generally columnar in 
shape, bear at their free extrem- 
ities little hair-like processes 
which are agitated incessantly 
with a lashing or vibrating mo- 
tion. These minute and delicate 
processes are named cilia^ and 
may be regarded as active prolon- 
gations of the cell-protoplasm. 

Fig. 8. — Glandular Epithelium, ^J^g manner in which cilia move 
WITH THE Cells set round a Simple . 

Saccular Gland. (Highly magnified.) IS best seen when they are not 
(Fiemmiug.) acting very quickly. The mo- 

tion of an individual cilium may be compared to the lash-like 
motion of a short-handled 
whip, the cilium being rap- 
idly bent in one direction. 
The motion does not involve 
the whole of the ciliated sur- 
face at the same moment, 
but is performed by the cilia 
in regular succession, giv- 
ing rise to the appearance of 
a series of waves travelling 

along the surface like the pio. 9. — ciliated Epithelium from the 
waves caused by the Avind Human Trachea. (Highly magnified.) a, 
n ^J c 1- i. 1X7-1, large ciliated cell ; d, cell, with two nuclei. 

m a field of wheat. When ^ 

they are in very rapid action, their motion conveys the idea of 

swiftly running water. 


Cilia have been shown to exist in almost every class of ani- 
mal, from the highest to the lowest. In man their use is to 
impel secreted fluids, or other matters, along the surfaces to 
which they are attached ; as, for example, the mucus of the 
trachea and nasal chambers, which they carry towards the out- 
let of these passages. 

Ciliated epithelium is found in the air passages, in parts of 
the generative organs, ventricles of the brain, and central canal 
of the spinal cord. 

To recapitulate : The most important situations in which a 
covering or lining of epithelial tissue is found in the body 
are : — 

1. On the surface of the integument, or external skin. 

2. On mucous membranes, or internal skin ; and in the 
recesses of secreting glands. 

3. On the inner surface of serous membranes, and on the 
inner surface of the heart, blood-vessels, and lymphatics. 

4. Lining the ventricles or cavities of the brain, and the 
central canal of the spinal cord. 

5. Epithelial cells, variously modified, are also found in the 
sensory terminations of the organs of special sense. 

Some varieties of epithelium are specially modified to form 
protective membranes ; others to elaborate or make secretions ; 
others, again, to form smooth linings for opposing surfaces ; 
others to keep surfaces moist ; and yet others to keep the 
surfaces they cover clean by sweeping outwards material that 
would otherwise accumulate and clog important passages. 

The hairs, nails, and the enamel of the teeth are modifica- 
tions of epithelial tissue. 



Following the classification of tissues we have adopted, the 
next group of tissues to be studied is that known as the con- 
nective tissue group. This includes : — 

Connective tissue proper. 
Adipose tissue or fat. 

These tissues differ considerably in their external character- 
istics, but are alike in that they all serve to connect and support 
the other tissues of the body ; they tend to pass imperceptibly 
the one into the other ; there are many points of similarity 
between the cells which occur in them, and we may, therefore, 
reasonably group them together. 

When connective tissue first begins to be formed as a distinc- 
tive tissue, the cells which are set apart to form it are round in 
shape and loosely packed together ; later these cells begin to 
throw out branches and to form a kind of network with open 
spaces. In these open spaces a semi-fluid substance is deposited 
which gradually becomes more consistent, and in this substance 
is developed the particular fibres which are the chief structural 
characteristics of connective tissue proper. 

Our description of epithelial tissue was briefly this : a skin 
or membrane formed of cells, which cells may be of a variety of 
shapes, and be arranged in one or more layers. It is distinctly 
a tissue of cells with very little of what we call intermediate or 
intercellular substance lying between the cells. Connective 




[Chap. III. 

tissue differs from epithelial tissue in having a great deal of 
intercellular substance between its cells, and according to the 
manner in which this intercellular substance develops do we 
get the different varieties of connective tissue. 

Connective tissue proper. — There are three principal varieties 
of connective tissue proper : viz. the areolar, the fibrous, and 
the elastic. 

Areolar tissue. — If we make a cut through the skin of some 
part of the body where there is no subcutaneous fat, as in the 
upper eyelid, and proceed to raise it from the parts lying beneath, 

Fig. 10. — Subcutaneous Areolar Tissue from a Young Rabbit. (Highly 
magnitied.) (E. A. S.) The white fibres are iu wavy bundles, the elastic fibres form 
an open network, p, p, vacuolated cells; g, granular cell; c, c, branching lamellar 
cells; c', a flattened cell, of which only the nucleus and some scattered granules are 
visible ; /, fibrillated cell. 

we observe that it is loosely connected to them by a soft filmy 
substance of considerable tenacity and elasticity. This is areolar 
tissue. It is also found, in like manner, under the serous and 
mucous membranes,^ and serves to attach them to the parts 
which they line or cover. Proceeding further, we find this 
areolar tissue lying between the muscles, the blood-vessels, and 
other deep-seated parts ; also forming investing sheaths for the 

1 These membranes line the internal cr.vities and surfaces of the body. 


muscles, the nerves, the blood-vessels, and other parts. It both 
connects and insulates entire organs, and, in addition, performs 
the same office for the finer parts of which these organs are made 
up. It is thus one of the most general and most extensively 
distributed of the tissues. It is, moreover, continuous through- 
out the body, and from one region it may be traced without 
interruption into any other, however distant, — a fact not with- 
out interest in practical medicine, seeing that in this way air, 
water, and other fluids, effused into the areolar tissue may spread 
far from the spot where they were first introduced or deposited. 

Areolar tissue, when its meshes are distended, appears to 
be composed of a multitude of fine threads and films crossing 
irregularly in every imaginable direction, leaving open spaces 
or areolce between them. Viewed with the microscope, these 
threads and films are seen to be principally made up of wavy 
bundles of exquisitely fine, transparent, white fibres, and these 
bundles intersect in all directions. Mixed with the white fibres 
are a certain number of elastic fibres, which do not form bun- 
dles, and have a straight instead of a wavy outline. The 
cells of the tissue, of which there 
are several varieties, lie in the 
spaces between the bundles of 

On comparing the areolar tissue 
of different parts, it is observed in 
some to be more loose and open in 
texture ; in others, more close and 
dense ; and accordingly free move- 
ment or firm connection between 
parts is provided for. 

Fibrous tissue. — Fibrous tissue is 
intimately allied in structure to ' '■'!} 

the areolar tissue, but the bundles // '' ■ < ■i-i 

of white fibres cohere very closely, ' ' , i ;, 

and instead of interlacing in every ^^^ ^^ _ f^^j^^us ' Tissue, from 

direction run for the most part in the Longitudinal Section of a 
1 , T ,• 1 ,1 Tendon. (After Gegeubauer.) 

only one or two directions, and thus 

confer a distinctly fibrous aspect on the parts which they com- 
pose. This fibrous tissue is met with in the form of ligaments, 
connecting the bones together at the joints, and in the form of 


sinews or tendons, by means of which the muscles are attached 
to the bones. It also forms fibrous membranes which invest 
and protect different parts or organs of the body. Examples 
of these are seen in the periosteum and perichondrium, which 
cover the bones and cartilages, and in the dura mater, which 
lines the skull and protects the brain. Fibrous membranes, 
called fascice, are also employed to envelop and bind down the 
muscles of different regions, of which the great fascia enclosing 
the muscles of the thigh and leg is a well-known example ; 
and, under the name of aponeuroses^ serve for the attachment of 
muscles in various parts of the body. It thus appears that 
fibrous tissue presents itself in the form of strong bands or 
cords, and of dense sheets or membranes. 

Fibrous tissue is white, with a peculiarly shining silvery 
aspect. It is exceedingly strong and tough, yet perfectly 
pliant ; but it is almost devoid of extensibility. By these qual- 
ities it is admirably suited to the purposes for which it is used 
in the human frame. By its inextensile character, and by its 
strength, it maintains in apposition the parts which it connects, 
and we find that the ligaments and tendons do not sensibly 
yield to extension in the strongest muscular efforts ; and though 
they sometimes snap asunder, it is well known that bones will 
break more readily than ligaments ; and the fibrous membranes 
or aponeuroses are equally strong, tough, and unyielding. 

Elastic tissue. — In elastic tissue the wavy white bundles are 
comparativel}'^ few and indistinct, and there is a proportionate 
development of the elastic fibres. When present in large num- 
bers they give a yellowish colour to the tissue. This form of 
connective tissue is extensile and elastic in the highest degree, 
but is not so strong as the fibrous variety, and breaks across the 
direction of its fibres when forcibly stretched. 

It occurs in its most characteristic form in what is called 
the ligamenta suhflava^ which forms an elastic band between 
some of the bones of the spine. Elastic tissue is also found in 
the walls of the air tubes and in the vocal cords ; it unites the 
cartilages of the larynx ; and enters largely into the formation 
of the walls of the blood-vessels, especially of the arteries. 

These three varieties of connective tissue agree closely with 
one another in elementary structure. It is the different ar- 
rangement of the cells and fibres, and the relative proportion of 

Chap. Ill,] 



one kind of fibre to the other, that gives them their different 
characteristics : the interlacing of the wavy bundles of finest 
fibres, giving us the delicate web-like areolar tissue ; the close 
packing of these bundles, giving us the dense opaque fibrous 
membranes and bands; and the preponderance of the elastic 
fibres, furnishing the extensile elastic tissue. 

This connective tissue proper, as we have already noted, is 
used for purely mechanical purposes : forming inextensile bands 
or pulleys ; strong protective membranes ; web-like, binding, and 
supporting material; sheaths of varying degrees of density; 
elastic bands or membranes ; and it also serves to carry the 
blood-vessels, lymphatics, and nerves to the parts which it 
connects and covers. 

Adipose tissue. — When fat first begins to be formed in the 
embryo, it is deposited in tiny droplets in some of the cells 

Fin. 12. — A Few Fat-Cells from the Margin of a Fat-Lobule. Very 
highly magnified, f.g. fat-globules distending a fat-cell ; n, nucleus; m, membran- 
ous envelope of the fat-cell; c, capillary vessel; v, veinlet; c.t. connective-tissue 
cell ; the fibres of the connective tissue are not shown. 

of the areolar connective tissue ; these droplets increase in size, 
and eventually run together so as to form one large drop 
in each cell. By further deposition of fat the cell becomes 
swollen out to a size far beyond that which it possessed orig 
inally until the protoplasm remains as a delicate envelope sur- 


rounding the fat drop. As these cells increase in number they 
collect into small groups or lobules, which lobules are for the 
most part lodged in the meshes of the areolar tissue, and are 
also supported by a fine network of blood-vessels. This fatty 
tissue exists very generally throughout the body, accompanying 
the still more widely distributed areolar tissue in most parts, 
though not in all, in which the latter is found. Still, its dis- 
tribution is not uniform, and there are some situations in which 
it is collected more abundantly. It forms a considerable layer 
underneath the skin, in the subcutaneous areolar tissue ; it is 
collected in large quantity around certain internal parts, espe- 
cially the kidneys ; it is seen filling up the furrows on the 
surface of the heart ; it is deposited beneath the serous mem- 
branes, or is collected between their folds ; collections of fat 
arie also common around the joints, padding and filling up 
inequalities ; and, lastly, fat exists in large quantities in the 
marrow of the long bones. 

Adipose tissue, unless formed in abnormal quantities, confers 
graceful outlines upon the human frame ; it also constitutes an 
important reserve fund, by storing up fatty materials, derived 
from the food and brought to it by the blood, in such a form 
and manner as to be readily reabsorbed into the circulation 
when needed. 

Cartilage. — This is the well-known substance called "gristle." 
When a very thin section is examined with a microscope, it is 
seen to consist of nucleated cells disposed in small groups in a 
mass of intercellular substance. This intercellular substance 
is sometimes transparent, and to all appearances homogeneous 
or structureless ; sometimes dim and faintly granular, like 
ground glass: both these conditions are found in what is called 
*' true " or hyaline cartilage, and which is the most typical form 
of the tissue. There is anotlier variety of cartilage, in which 
the intercellular substance is everywhere pervaded with fibres. 
When the fibres are of the white variety, it is called white 
fibro-cartilage ; when they are elastic fibres, it is called yellow 
or elastic fibro-cartilage. 

Although cartilage can be readily cut with a sharp knife, it 
is nevertheless of very firm consistence, but at the same time 
highly elastic, so that it readily yields to extension or pressure, 
and immediately recovers its original shape when the con- 

Chap. III.] 





straining force is withdrawn. By reason of these mechanical 
properties it serves important purposes in the construction of 
some parts of the body. 

Hyaline cartilage occurs chiefly 
in two situations ; viz. covering 
the ends of the bones in the 
joints, where it is known as 
articular cartilage, and forming 
the rib cartilages, where it is 
known as costal cartilage. In 
both these situations the carti- 
lages are in immediate connec- 
tion with bone, and may be said 
to form part of the skeleton. 
The articular cartilages, in cov- 
ering the ends or surfaces of 
bones in the joints, provide these 
harder parts with a smooth and 
yielding surface, the smoothness 
giving ease to the motion of the 
joint, and the elastic yielding sur- 
face breaking the force of con- 
cussions. The costal cartilages, 
in forming a considerable part of 
the solid framework of the thorax or chest, impart elasticity to 
its walls. Cartilage also enters into the formation of the nose, 
ears, larynx, and windpipe. It strengthens these parts without 
making them unduly rigid, maintains their shape, keeps them 
permanently open, and gives attachment to moving muscles and 
connecting ligaments. 

Elastic or yellow fibro-cartilage is tougher and more flexible 
than hyaline cartilage ; it occurs only in parts of the throat 
and ear. 

White fibro-cartilage is found wherever great strength com- 
bined with a certain amount of rigidity is required; thus we 
find it joining bones together, the most familiar instance being 
the flat round plates or disks of fibro-cartilage connecting the 
bones of the spine and the pubic bones. White fibro-cartilage 
very closely resembles white fibrous tissue. 

Cartilage is not supplied with nerves, and very rarely with 

Fig. 13. — Articular Hyalinb 
Cartilage from the Femur of an 
Ox. s, intercellular substance; p, 
protoplasmic cell ; n, nucleus. (Ran- 


blood-vessels. Being so meagrely supplied with blood the vital 
processes in cartilage are very slow, and when a portion of it is 
absorbed in disease or removed by the knife, it is regenerated 
very slowly. A wound in cartilage is usually at first healed by 
connective tissue proper, which may or may not become grad- 
ually transformed into cartilage. Nearly all cartilages receive 
their nourishment from the perichondrium which covers them, 
and which is a moderately vascular fibrous membrane. 

Bone. — Bone is a connective tissue in which the intercellular 
or ground substance is rendered hard by being impregnated 
with mineral salts. 

On sawing up a bone it will be seen that it is in some parts 
dense and close in texture, appearing like ivory, whilst in others 
it is open and spongy, and we distinguish two forms of bony 
tissue, the dense or compact, and the spongy or cancellated. 
On closer examination, however, it will be seen that the bony 
matter is everywhere porous, and that the difference between 
the two varieties of tissue arises from the fact that the compact 
tissue has fewer spaces and more solid matter between them, 
and that the cancellated has larger cavities and more slender 
intervening bony partitions. In all bones the compact tissue 
is the stronger ; it lies on the surface of the bone and forms an 
outer shell or crust, whilst the lighter spongy tissue is con- 
tained within. The shafts of the long bones are almost entirely 
made up of the compact substance, except that they are hol- 
lowed out to form a central canal — the medullary canal — 
which contains the marrow.^ Marrow is also found in the 
spongy portions of the bone in the spaces between the bony 

The hard substance of all bone is arranged in bundles of 
bony fibres or lamellce, which in the cancellated texture join 
and meet together so as to form a structure resembling lattice- 
work (cancelli)^ and whence this tissue receives its name. In 
the compact tissue these lamelhie are usually arranged in rings 
around canals which carry blood-vessels in a longitudinal direc- 
tion through the bones. Between the lamellae are branched 

1 There are two kinds of marrow, red and yellow. Red marrow contains, 
in 100 parts, 75 of water and 25 of solids, the solids consisting of albumin, 
fibrin, extractive matter, salts, and a mere trace of fat. Yellow marrow con- 
tains, in 100 parts, 96 of fat, 1 of areolar tissue and vessels, and 3 of fluid. 

Chap. III.] 



cells which lie in cell-spaces or cavities called lacunce, and run- 
ninof ont in a wheel-like or radial direction from each lacuna 
are numerous tiny canals or canaliculi connecting one cell-space 
or lacuna with another, and forming a system of minute inter- 
communicating channels. 

All bones are covered by a vascular fibrous membrane, the 
periosteum, and, unlike cartilage, the bones are plentifully sup- 
plied with blood. If 
we strip this perios- 
teum from a fresh 
bone, we see many 
bleeding points repre- 
senting the apertures 
through which the 
blood-vessels enter the 
bone. After entering, 
the blood runs through 
short longitudinal 
channels which com- 
municate freely with 
one another, and are 
called, from the name 
of their discoverer, 
Haversian canals. 
Around these Haver- 
sian canals, as we have 
already stated, the la- 
mellae are disposed in 
rings, while the lacunae 
containing the bone- 
cells are also arranged, 
between the lamellce, 
in circles around the 
canals. As the canaliculi run in a radial direction from the 
lacunce across the lamellse, it follows that the innermost ones 
must run into the Haversian canals, so that there is a direct 
communication between the blood in these canals and the cells 
in all the lacunse connected with and surrounding each Haver- 
sian canal. In this way the whole substance of the bone is 
penetrated by intercommunicating channels, and nutrient mat- 

FiG. 14. — Transverse Section of Compact 
Tissue (of Humerus). (Masnified about 150 diam- 
eters.) (Sharpey.) Three of the Haversian canals 
are seen, with their concentric rings faintly indi- 
cated ; also the lacunae, with the canaliculi extend- 
ing from them across the direction of the encircling 
lamellse, or concentric rings. 


ters and mineral salts from the blood in the Haversian canals 
can find their way to every part. 

The mineral or earthy substance which is deposited in bone, 
and which makes it hard, amounts to about two-thirds of the 
weight of the bone. It consists chiefly of phosphate of lime, 
with about a fifth part of carbonate of lime, and a small portion 
of other salts. The soft or animal matter consists chiefly of 
blood-vessels and connective tissue, and may be resolved by boil- 
ing almost entirely into gelatine : it constitutes about one-third 
of the weight of the bone. 

In the reunion of fractured bones new bony tissue is formed 
between and around the broken ends, connecting them firmly 
together; and when a portion of bone dies, the dead part be- 
comes separated from the living bone, and if thrown off or 
removed, a growth of new bone very generally takes place to 
a greater or less extent. The periosteum is largely concerned 
in the nutrition and repair of bone ; for if a portion of the 
periosteum be stripped off, the subjacent bone will be liable to 
die, while if a large part or the whole of a bone be removed, 
and the periosteum at the same time left intact, the bone will 
wholly, or in a great measure, be regenerated. 

In the embryo the foundation of the skeleton is laid in cartilage, or in primi- 
tive membranous connective tissue, ossification of the bones occurring later. 
The hardening or ossification of the bones is accomplished by the penetration of 
blood-vessels and bone-cells, called osteo-blasts, from the periosteum. As they 
penetrate into the cartilaginous or membranous models, they absorb the car- 
tilage and connective tissue and deposit the true bone tissue at various points 
until they form the particular bony structure with which we are familiar. 



The bones are the principal organs of support, and the pas- 
sive instruments of locomotion. Connected together in the 
skeleton, they form a framework of hard material, affording 
attachment to the soft parts, maintaining them in their due 
position, sheltering such as are of delicate structure, giving sta- 
bility to the whole fabric, and preserving its shape. 

The entire skeleton in the adult consists of two hundred dis- 
tinct bones. These are : — 

The spine, or vertebral column (sacrum and coccyx 

included) 26 

Cranium 8 

Face 14 

Os hyoides, sternum, and ribs 26 

Upper extremities 64 

Lower extremities 62 


In this enumeration the patellce, or knee-pans, are included as 
separate bones, but the smaller sesamoid bones, and the small 
bones of the ear, are not included. 

These bones may be divided, according to their shape, into 
four classes : Long, Short, Flat, and Irregular. 

The long and short bones are found in the extremities. The 
flat and irregular bones are found in the trunk and head, with 
the exception of the patellce, which are two small flat bones 
found in the lower extremities, and the scapulce, which are also 
two flat bones usually reckoned among the bones of the upper 

The bones of the trunk and head are used chiefly to form 




[Chap. IV. 

cavities and to support and 
protect the organs contained 
in these cavities. The bones 
of the extremities enclose no 
cavities, and are chiefly used 
in the upper extremity for 
tact and prehension, and in 
the lower for support and 
locomotion ; in both situa- 
tions they form a system of 
levers. If the surface of any 
bone is examined, certain 
eminences and depressions 
are seen, which are of two 
kinds : articular and non- 
articular. Non-articular pro- 
cesses and depressions serve 
for attachment of ligaments 
and muscles ; the articular 
are provided for the mutual 
connection of joints. 

Long bones. — A long bone 
consists of a lengthened 
cylinder or shaft and two 
extremities. The shaft is 
formed mainly of compact 
tissue, this compact tissue 
beingf thickest in the mid- 
die where the bone is most 
slender and the strain great- 
est, and it is hollowed out 
in the interior to form the 
medullary canal. The ex- 
tremities are made up of 

vr^ ir. T„„, a^„,„^^, -ti spongy tissue with only a 

tiG. 15. — The Skeleton, or, parietal '■ '=>-' •' 

bone; 6, frontal; c, cervical vertebrte; d, thin COating of COmpact Sub- 

sternum; Mumbar vertebra. ;/, ulna; fir, ra- ^^ .^^^^ ^^,^ ^^^^ ^^ j^^g 

dius ; n, wrist or carpal bones ; t, metacarpal 

bones; A;, phalanges ; ;, tibia; jh, fibula; ?i, expanded for greater COn- 

tarsal bones; o metatarsal; p phalanges; ^gnience of mutual COnnec- 
q, patella; r, femur; s, haunch bone; t, 

humerus; u, clavicle. tion, and to afford a broad 

Chap. IV.] THE SKELETON. 25 

surface for muscular attachment. All long bones are more or 
less curved, which gives them greater strength and a more 
graceful outline. 

Short bones. — The short bones are small pieces of bone 
irregularly shaped. Their texture is spongy throughout, ex- 
cepting at their surface, where there is a thin crust of compact 

Flat bones. — Where the principal requirement is either exten- 
sive protection or the provision of broad surfaces for muscular 
attachment, the bony tissue expands into broad or elongated 
flat plates. The flat bones are composed of two thin layers of 
compact tissue, enclosing between them a variable quantity of 
cancellous tissue. In the bones of the skull this outer layer 
is thick and tough; the inner one, thinner, denser, and more 
brittle. The cancellated tissue lying between the two layers, 
or " tables of the skull," is called the diploe. 

Irregular bones. — The irregular bones are those which, on 
account of their peculiar shape, cannot be grouped under either 
of the preceding heads. 

Bones of the upper extremity : — ■ 

Clavicle (collar bone) 2 

Scapula (shoulder blade) 2 

Humerus (arm) 2 

Ulna, 2 ) .„ ^ 

Kadius,2y(^°^-^^^'^) ^ 

Carpus (wrist) 16 

Metacarpus (palm of hand) „ . 10 

Phalanges (fingers) 28 

Thus enumerated we see that the bones of the upper extrem- 
ity consist of the shoulder girdle (clavicle and scapula), of the 
arm, the forearm, and the hand ; the bones of the hand being 
further subdivided into those of the wrist, the palm of the hand, 
and the fingers. 

The clavicle forms the anterior portion of the shoulder girdle. 
It articulates by its inner extremity with the sternum, and by 
its outer extremity with the acromion process ^ of the scapula. 

1 All eminences and projections of bones are termed processes, and these 
processes were named by the early anatomists, either from their shape or use, 
or from their fancied resemblance to some well-known object. It is well to look 



[Chap. IV. 

Fig. 16. — The Clavicle 

In the female the clavicle is generally less curved, smoother, 
and more slender than in the male. In those persons who 

perform considerable 
manual labour, which 
brings into constant 
action the muscles con- 
nected with this bone, 
it acquires considerable 

The scapula, or shoul- 
der blade, forms the 
back part of the shoul- 
der girdle. It is a large 
flat bone, triangular in 
shape, placed between 
the second and seventh, 
or sometimes eighth, 
ribs on the back part 
of the thorax. It is 
unevenly divided on its 
dorsal surface by a very 
prominent ridge, the 
spine of the scapula, 
which terminates in a 
large triangular projec- 
tion called the acromion 
process, or summit of 
the shoulder. Below 

„ the acromion process, 

FiQ. 17. — The Scapula. 1, glenoid cavity ; - i, i j f 

2, end of the spine of scapula. and at the liead 01 

up the meaning of these Greek or Latin words which are used so plentifully in 
naming all parts of the skeleton ; the whole subject will become more interest- 
ing, more readily understood, and more easily remembered. A glossary for this 
purpose is added at the end of the book. 

Chap. IV.] 








the shoulder blade is a shallow socket, the glenoid cavity, which 
receives the head of the humerus. 

The humerus is the longest and 
largest bone of the upper limb. 
The upper extremity of the bone 
consists of a rounded head joined 
to the shaft by a constricted neck, 
and of two eminences called the 
greater and lesser tuberosities. The 
head articulates with the glenoid 
cavity of the scapula. The con- 
stricted neck above the tuberosities 
is called the anatomical neck, and 
that below the tuberosities the sur- 
gical neck, from its being often the 
seat of fracture. The lower ex- 
tremity of the bone is flattened 
from before backwards into a broad 
articular surface, which is divided 
by a slight ridge into two parts, by 
means of which it articulates with 
ulna and radius. 

The ulna (elbow bone) is placed 
at the inner side of the forearm, 
parallel with the radius. Its upper 
extremity presents for examination 
two large curved processes and two 
concave cavities; the larger process 
forms the head of the elbow, and 
is called the olecranon process. The 
lower extremity of the ulna is of 
small size, and is excluded from the 
wrist by a piece of fibro-cartilage. 

The radius is situated on the outer 

side of the forearm. The upper Fig.IS.- The Humerus, a, 

^ J- rounded head ; gt, greater tuber- 

end is small and rounded with a osity; it, lesser tuberosity; b, 

shallow depression on its upper sur- fZlV""' ^"^'^'"'"' ^^ ^'''^^^ 
face for articulation with the hume- 
rus, and a prominent ridge about it, like the head of a nail 
by means of which it rotates within the lesser sigmoid cav- 







[Chap. IV. 

ity of the ulna. The lower end of the radius is large, and 
forms the chief part of the wrist. 

The carpus, or wrist, is formed of 
small pieces of bone united by liga- 
ments ; they are arranged in two 
rows and are closely welded to- 
gether, yet by the arrangement of 
their ligaments allow of a certain 
amount of motion. There are eight 
carpal bones in each wrist; they are 
named from their shape, scaphoid, 
semilunar, cuneiform, etc. 

Each metacarpus is formed by five 
bones. These metacarpal bones are 
curved longitudinally, so as to be 
convex behind, concave in front ; 
they articulate by their bases with 
the bones of the wrist and with one 
another, and the heads of the bones 
articulate with the phalanges. 

The phalanges, or digits, are the 
bones of tlie fingers; they are four- 
teen in number (in each hand), 
three for each finger, and two for 
the thumb. The first row articu- 
lates with the metacarpal bones and 
the second row of phalanges ; the 
second row, with the first and third; 
and the third, with the second row. 
Bones of lower extremity : — 

Os innominatum (hip bone) ... 2 

Femur (thigh bone) 2 

o, olecranon process, on the -t atella (knee pan) Zi 

anterior surface of which are Tibia, '^ \ n \ a 

seen the large (r/s) and the JTibula 2 i ^ ^^^ 

small {Is) cavities for the recep- m ' / i i \ -\ a 

tion of the lower end of the TaiSUS (ankle) . 14 

humerus and of the head of Metatarsus (soIe and instep of foot) . 10 

the radius, respectively; h, Phalanges (toes) 28 

head of radius. o \ / — 


The bones of the lower extremity correspond to a great 
extent with those of the upper extremity, and bear a rough 

Thk Ulna and 
radius; 2, ulna; 

Chap. IV.] 



resemblance to them. They consist, as stated above, of the 
OS innominatum, which forms the pelvic girdle connecting 
the lower extremity with the trunk, of the thigh, the leg, 
and the foot. The foot is separable into ankle, sole and 
instep, and toes. 

The OS innominatum, or nameless bone, so called from bear- 
ing no resemblance to any known object, is a large irregular- 
shaped bone, which, with its fellow of the opposite side, forms 
the sides and front wall of the pelvic cavity. In young 

Fig. 20. — Bones of the Wrist and Hand, m, metacarpal bones ; 
p, phalanges; 3, bones of the wrist. 

subjects it consists of three separate parts, and although in 
the adult these have become united, it is usual to describe 
the bone as divisible into three portions, — the ilium, the 
ischium, and the pubes. The ilium, so called from its sup- 
porting the flank, is the upper broad and expanded portion 
which forms the prominence of the hip. The ischium is the 
lower and strongest portion of the bone, while the pubes is 
that portion which forms the front of the pelvis. Where 
these three portions of the bone meet and finally ankylose is 
a deep socket, called the acetabulum, into which the head of 



[Chap. IV. 

the femur fits. Other points of special interest to note are 
(1) the spinous process formed by the projection of the crest 
of the ilium in front, which is called the anterior superior 
spinous process, and which is a well-known and convenient 
landmark in making anatomical measurements ; (2) the largest 

Fig. 21. — Os Innominatum. Outer surface. R, O, crest of ilium, just below 
is seen the anterior superior spinous process ; J, tuberosity of ischium ; T, part of 
pubes, between J and T is seen the thyroid foramen : //, acetabulum, beloAv H is 
seen end of pubic bone which, with its fellow of opposite side, forms the symphysis 
pubis. (For further illustration, vide Figs. 46 and 47.) 

foramen in the skeleton, known as the door-like or thyroid 
foramen, situated between the ischium and pubes ; and (3) the 
symphysis pubis, or pubic articulation, which also serves for 
a convenient landmark in making measurements. 

The femur is the longest, largest, and strongest bone in the 
skeleton. In the erect position it is not vertical, the upper 

Chap. IV.] 



end being separated from its 
fellow by a considerable inter- 
val, which corresponds to the 
entire breadth of the pelvis, 
but the bone inclines gradu- 
ally downwards and inwards, 
so as to approach its fellow 
towards its lower part, in order 
to bring the knee-joint near the 
line of gravity of the body. The 
degree of inclination varies in 
different persons, and is greater 
in the female than the male, on 
account of the greater breadth 
of the pelvis. The upper ex- 
tremity of the femur, like that 
of the humerus, consists of a 
rounded head joined to the 
shaft by a constricted neck, and 
of two eminences, called the 
greater and lesser trochanters. 
The head articulates with the 
cavity in the os innominatum, 
called the acetabulum. The 
lower extremity of the femur is 
larger than the upper, is flat- 
tened from before backwards, 
and divided into tAvo large emi- 
nences or condyles by an inter- 
vening notch. It articulates 
with the tibia and the patella, 
or knee-pan. 

The patella, or knee-cap, is 
a small flat triangular bone 
placed in front of the knee- 
joint, which it serves to pro- 
tect. It is separated from the 
skin by a bursa. (See page 51.) 

The tibia is situated at the front and inner side of the leg, and 
forms what is popularly known as the shin bone. In the male, its 

Fig. 22. — The Femur, b, rounded 
head; 7i, neck; jr^r, greater trochanter ; 
Itr, lesser trochanter. 



[Chap. IV. 

direction is vertical and parallel 
with the bone of the opposite side ; 
but in the female it has a slight 
oblique direction outwards, to com- 
pensate for the oblique direction of 
the femur inwards. The upper ex- 
tremity is large, and expanded into 
two lateral eminences with concave 
surfaces which receive the condyles 
of the femur. The lower extrem- 
ity is much smaller than the upper; 
it is prolonged downwards on its 
inner side into a strong process, 
the internal malleolus. It articu- 
lates with the fibula and one of the 
bones of the ankle. 

The fibula is situated at the outer 
side of the leg. It is the smaller 
of the two bones, and, in propor- 
tion to its length, the most slender 
of all the long bones : it is placed 
nearly parallel with the tibia. The 
upper extremity consists of an ir- 
regular quadrate head by means of 
which it articulates with the tibia. 
The lower extremity is prolonged 
downwards into a pointed process, 
the external malleolus, which lies 
just beneath the skin. It articu- 
lates with the tibia and one of the 
bones of the ankle. 

The tarsus, or ankle, like the 
carpus, or wrist, is composed of 
small pieces of bone united by 
ligaments, but the tarsal bones 
differ from the carpal in being 
larger and more irregularly shaped. 
The largest and strongest of the tarsal bones is called the 
OS calcis, or heel bone ; it serves to transmit the weight of 
the body to the ground, and forms a strong lever for the 

Fig. 23.— The Tibia and Fibula. 
o, tibia; /, fibula; etu and itu, lat- 
eral eminences for reception of con- 
dyles of femur; h, head of fibula; 
em, external malleolus; im, internal 

Chap. IV.] 



muscles of the calf of the leg. There are seven tarsal bones 
in each ankle. (The names of the carpal and tarsal bones are 
supplied in the table of the bones at the end of the chapter.) 

The metatarsus is formed by live bones. These metatarsal 
bones closely resemble the metacarpal bones of the hand. Each 
bone articulates with the tarsal bones 
by one extremity, and by the other 
with the first row of phalanges. 

The phalanges of the foot, both in 
number and general arrangement, 
resemble those in the hand, there 
being two in the great toe and three 
in each of the other toes. 

Bones of the cranium : — 

Occipital 1 

Parietal 2 

Frontal 1 

Temporal 2 

Sphenoid 1 

Ethmoid 1 


The occipital bone is situated at 
the back and base of the skull. At 
birth the bone consists of four parts, 
which do not unite into a single bone 
until about the sixth year. The in- 
ternal surface is deeply concave, and 
presents many eminences and de- 
pressions for the reception of parts 
of the brain. There is a large 
hole — the foramen magnum — in 
the inferior portion of the bone, for 
the transmission of the medulla oblongata, the constricted por- 
tion of the brain where it narrows down to join the spinal cord. 

The parietal bones (^paries, a wall) form by their union the 
greater part of the sides and roof of the skull. The external 
surface is convex and smooth ; the internal surface is con- 
cave, and presents eminences and depressions for lodging the 
convolutions of the brain, and numerous furrows for the rami- 
fications of arteries. 

Fig. 24. — Bones of the 
Ankle and Foot. m, meta- 
tarsal boues; p, phalanges; ca, 
OS calcis, or heel bone. 

Fig. 25. — Occipital Bone. luner surface. 9, 9, and 10, 10, depressions for reception 
of lobes of brain ; 11, foramen magnum. 

Fig. 26. — Parietal Bone. Inner surface, ^.parietal depression; £, furrow for 

ramification of arteries. 


Chap. IV.] 



Fig. 27. — Frontal Bone. Outer surface. 1, frontal emi- 
nence ; 7, roof of orbital cavity ; 10, orbital arch. 

The frontal bone resembles a cockle shell in form. It not 
only forms the forehead, but also enters into the formation of 

the roof of the 

orbits, and of 
the nasal cavity. 
The arch formed 
by part of the 
frontal bone 
over the eye 
is sharp and 
prominent and 
affords that or- 
gan considera- 
ble protection 
from injury. 
At birth the bone consists of two pieces, which afterwards 
become united, along the middle line, by a suture which runs 
from the vertex of the bone to the root of the nose. This 

suture usually 
becomes obliter- 
ated within a 
few years after 
birth, but it occa- 
sionally remains 
throughout life. 
The temporal 
bones are situ- 
ated at the sides 
and base of the 
skull. They are 
named temporal 
from the Latin 
word, tempus, 
time, as it is on 
the temple the 
hair first be- 
comes gray and thin, and thus shows the ravages of time. 
The temporal bones are divided into three parts : the hard, 

1 The temporal, sphenoid, lachrymal, vomer, and maxillary bones are drawn 
to a larger scale than the other bones of the head and face. 

Fig. 28. —Temporal Bone.i 1, squamous portion; 2, 
placed below external opening of auditory canal in petrous 
portion : 3, placed below mastoid portion ; 4, placed below 
glenoid cavity for reception of condyle of lower jaw. 



[Chap. IV. 

dense portion, called petrous; a thin and expanded scale-like 
portion, called squamous ; and a mastoid portion, which is per- 
forated by numerous holes and contains a number of sinuses or 

Fig. 29. — Sphenoid Bone, a, greater wing; b, lesser wing. 

air spaces. The internal ear, the essential part of the organ 
of hearing, is contained in a series of cavities, channelled out of 
the substance of the petrous portion. Between the squamous 

and petrous portions is a socket for 
the reception of the condyle of the 
lower jaw. 

The sphenoid bone {sphen, a wedge) 
is situated at the anterior part of the 
base of the skull, articulating with all 
the other cranial bones, which it binds 
firmly and solidly together. In form 
it somewhat resembles a bat with ex- 
tended wings. 

The ethmoid bone is an exceedingly 
light, spongy bone, placed between the 
two orbits and at the root of the nose, 
contributing to form a part of each of 
these cavities. The portion of the bone 
situated at the back of the nose, which forms the roof of the 
nasal fossae and also closes the anterior part of the base of 
the skull cavity, is pierced by numerous holes, through which 

Fig. 30. — E j;hmoii> Bone 
Posterior surface. 2, cribri 
form, or perforated plate. 

Chap. IV.] THE SKELETON. 37 

the nerves conveying the sense of smell pass. Descending 
from this perforated plate, on either side of the nasal cavity, 
are two masses of very thin, spongy, bony tissue. 
Bones of the face : — 

Nasal 2 

Lachrymal 2 

Vomer 1 

Malar 2 

Palate 2 

Inferior turbinated 2 

Superior maxillary 2 

Inferior maxillary 1 


The nasal bones are two small oblong bones, 
varying in size and form in different individ- 
uals; they are placed side by 
r>^-,ft side at the middle and upper 

■ ■■" "tA part of the face, forming by their %; 

i unction " the bridge " of the 

Fig. 31. — Na- 
^^^^- SAL Bone. Outer 

The lachrymal are the smallest surface. J.inter- 

1 j^ £ ^^ 1 <• .1 iial border; £, 

ana most iragiie bones oi the external border. 
Fig. 32. — Lach- face. They are situated at the 

front part of the inner wall of the orbit, and 
resemble somewhat in form, thinness, and size, a finger-nail. 

The vomer is a single bone 
placed at the back part of ^—-'^'^fi \\ 

the nasal cavity, and forms /■ .> / , -xxv 

part of the septum of the t-""^"'. ^;^. 

na^al fossse. It is thin, /^'',:^^^^'''' • '/''^'W 

and shaped somewhat like a ,:::^:^0'' --" ' -■'■■'■'■'■'■ 'i,''''^^i'.-M^ 

ploughshare, but varies in %^. — — ■ " .■■'''-^■' v-^ii 

different individuals, being 
frequently bent to one or 

^ "^ Fig. 33. — Vomer. 

the other side. 

The malar or cheek bones form the prominence of the cheek, 
and part of the outer wall and floor of the orbit. 

The palate bones form (1) the back part of the roof of the 
mouth ; (2) part of the floor and outer wall of the nasal fossse; 
and (3) a very small portion of the floor of the orbit. 



[Chap. IV. 

The inferior turbinated bones are situated on the outer wall 
of each side of the nostril. Each consists of a layer of thin, 

Fig. 34. — Malar Bone. 

Fig. 35. — Palate Bone. 

Fig. 30. — Inferior Tureinated 
Bone. Convex surface. 

spongy bone, curled upon itself like a scroll ; hence its name, 


The superior maxillary is one of the most important bones 

of the face, in a surgical point of 
view, on account of the number of 
diseases to which some of its parts 
are liable. With its fellow of the 
opposite side, it forms the whole of 
the upper jaw. Each bone assists 

in forming part of the floor of the orbit, the floor and outer 

wall of the nasal fossoe, 

and the greater part of the 

roof of the mouth. That 

part of the bone which con- 
tains the teeth is called the 

alveolar process, and is exca- 

vat€id into cavities, varying 

in depth and size according 

to the size of the teeth they 

contain. There are eight 

cavities in each bone: those 

for the canine teeth are 

the deepest ; those for the 

molars are widest and sub- 
divided into minor cavities; 

those for the incisors are 

single, but deep and narrow. 

""'Xe. Bicuspids 

Fig. 37. — Superior Maxillary Bone. 
1, orbital surface; 2, facial surface; 3, alveo- 
lar process. 

Chap. IV.] 



Coronoid process. 

The inferior maxillary, or lower jaw, is the largest and 

strongest bone of the face, and serves for 

the reception of the lower teeth. At birth, 

it consists of two lateral halves, which 

join and form one bone during the first or 

second year. The lower jaw undergoes 

several changes in shape during life, owing 

mainly to the hrst 

and second denti- 
tion, to the loss of 

teeth in the aged, 

and the subsequent 

absorption of that 

part of the bone 

which contained 

them. It articulates, by its condyles, with the sockets in the 

temporal bones. 

The hyoid, os hyoides, or tongue bone, is an isolated, U-shaped 
bone lying in front of the throat, just above 
"Adam's apple"; it supports the tongue, and 
gives attachment to some of its numerous 

The spine or vertebral column is formed of a 
series of bones called vertebrse. The vertebrae 

are thirty-three in number, and according to the position 

they occupy are named : — 

Cervical 7 

Dorsal 12 

Lumbar 5 

Sacral 5 

Coccygeal 4 


Fig. 39.— Hyoid 

The vertebrre in the upper three portions of the spine are 
separate throughout the whole of life ; but those found in 
the sacral and coccygeal regions are, in the adult, firmly 
united, so as to form two bones, five entering into the upper 
bone, or sacrum, and four into the terminal bone of the spine, 
or coccyx. 

Each vertebra consists of two essential parts, an anterior 



[Chap. IV. 

solid portion or body, and a posterior portion or arch. The 
bodies of the vertebroe are piled one upon another, forming a 
solid, strong pillar, for the support of the cranium and trunk, 
the arches forming a hollow cylinder behind for the protection 
of the spinal cord. Each arch has seven processes : four 
articular, two transverse, and one spinous process. The dif- 
ferent vertebrae are connected together by means of the articu- 
lar processes, and by disks of intervertebral fibro-cartilage 
placed between the vertebral bodies, while the transverse and 
spinous processes serve for the attachment of muscles which 
move the different parts of the spine. In the cervical region of 

the vertebral column 
the bodies of the ver- 
tebras are smaller than 
in the dorsal, but the 
arches are larger ; the 
spinous processes are 
short, and are often 
cleft in two, or bifid. 
The first and second 
cervical vertebrse 
differ considerably 
from the rest. The 
first, or atlas, so 
named from support- 
ing the head, has 
practically no body, 
and may be described as a bony ring divided into two sections 
by a transverse ligament. The dorsal section of this ring 
contains the spinal cord, and the ventral or front section 
contains the bony projection which arises from the upper sur- 
face of the body of the second cervical vertebra, or axis. This 
bony projection, called the odontoid process, represents the 
body of the atlas. Around this peg the atlas rotates when 
the head is turned from side to side, carrying the skull, to 
which it is firmly articulated, with it. The bodies of the dorsal 
vertebras are larger and stronger than those of the cervical ; 
they contain depressions for the reception of the vertebral 
ends of the ribs. The bodies of the lumbar vertebrse are the 
largest and heaviest in the whole spine. The sacrum, formed 

Fig. 40. — A Cervical Vertebra. Inferior sur- 
face. 1, spinous process, slightly bifid ; 4, transverse 
process ; 5, articular process, inferior surface. Below 
the arch, or hollow portion, is seen the solid portion, 
or body. 

Chap. IV.] 



by the union of the five sacral vertebrse, is a large triangular 
bone situated like a wedge between 
the ossa innominata ; it is curved 
upon itself in such a way as to give 
increased capacity to the pelvic 
cavity (^vide Fig. 47). The coccyx 
is usually formed of four small seg- 
ments of bone, and is the most 
rudimentary part of the vertebral 

The vertebral column as a whole. — 
Tlie spinal column in a man of aver- 
age height is about twenty-eight 
inches long. Viewed from the side 
it presents four curvatures; the first 
curve has its convexity forwards in 
the cervical region, and is followed 
in the dorsal, by a curve with its a- 
concavity towards the chest. In the 
lumbar region the curve has again 
its convexity forwards, while in the 
sacral and coccygeal regions the con- 
cavity is turned forwards. These 
curvatures confer a considerable 
amount of springiness and strength 
upon the spinal column which would 
be lacking were it a straight column : 
the elasticity is further increased by 
the disks of fibro-cartilage lying be- 
tween and connecting the bodies of 
the vertebroe. These disks or pads 
also mitigate the effects of concussion 
arising from falls or blows, and allow 
of a certain amount of motion be- iporrct. 

tween the vertebras. The amount Fig. 4i. — Side View of Spi- 

Of motion permitted is greatest in ^^^ Column, without Sacrum 

^ => AND Coccyx. 1 to 7, cervical 

thp cervical region. Between each vertebrEe; 8 to 19, dorsal verte- 

P , 1 ^ 1. i\ 1 brse; 20 to 24, lumbar vertebrae; 

pair of vertebrse are apertures through ^^ ^^ ^pi^^,^, processes; (7, B, 

which the spinal nerves pass from transverse processes; E, inter- 
, , . , 1 vertebral aperture or foramen : 

the spinal cord. l^ atlas; 2, axis. 



[Chap. IV. 

The thorax, or chest, is an elongated conical-shaped cage, 
formed by the sternum and costal cartilages in front, the 
twelve ribs on each side, and the bodies of the twelve dorsal 


Fig. 42. — Thorax. 1 to 12, ribs; c/, d, costal cartilages ; c, upper end of sternum; 
6, middle portion of sternum; la, first dorsal vertebra; 12 «, twelfth dorsal verte- 
bra ; 7 a, seventh cervical vertebra ; 1 to 7, true ribs ; 8 to 12, false ribs : 11, 12, float- 
ing ribs. 10th rib is defective ; it should be attached to the costal cartilage. 

vertebrae behind. It contains and protects the 23rincipal organs 
of respiration and circulation. 

The sternum, or breast bone, is a flat narrow bone, situated 
in the median line in the front of the chest, and consisting, 
in the adult, of three portions. It has been likened to an 
ancient sword. The ui)per piece, rejDresenting the handle, is 

Chap. IV.] 



termed the manubrium or handle ; the middle and largest 
piece, which represents the chief part of the blade, is termed 
the , gladiolus ; and the inferior piece, which is likened to the 
point of the sword, is termed 
the ensiform appendix. On 
both sides of the upper and 
middle pieces are notches for 
the reception of the sternal 
ends of the costal cartilages. 
The ensiform appendix is carti- 
laginous in structure in early 
life, but is more or less ossified 
at the upper part in the adult : 
it has no ribs attached to it. 
The sternum is about six inches 
long, being rather longer in the 
male than in the female. 

The ribs are elastic arches of 
bone, forming the chief part of 
the thoracic wall (^vide Fig. 42). 
They are usually twelve in 
number on each side. They 
are all connected behind with 

the vertebrae, and the first seven pairs are connected with the 
sternum in front through the intervention of the costal carti- 
lages: these first seven pairs are called from their attachment 
the vertebro-sternal, or true ribs. The remaining five pairs 
are termed false ribs; of these, the first three, being attached 
in front to the costal cartilages, are usually called the vertebro- 
costal, while the two remaining, being unattached in front, 
are termed vertebral, or floating ribs. The convexity of the 
ribs is turned outwards so as to give roundness to the sides of 
the chest and increase the size of its cavity; each rib slopes 
downwards from its vertebral attachment, so that its sternal 
end is considerably lower than its dorsal. The spaces left 
between the ribs are called the intercostal spaces. 

The skull as a whole. — The skull, formed by the union of 
the cranial and facial bones already described, is divisible into 
cranium or brain case, and the anterior region or face. 

The bones of the cranium begin to develop at a very early 

Fig. 43. — Sternum. Front and side 



[Chap. IV. 

period of foetal life. Before birth the bones at the top and 
sides of the skull are separated from each other by membra- 
nous tissue in which bone is not yet formed. The spaces 
at the angles of the bone occupied by this membranous tissue 
are termed the fontaiielles, so named from the pulsations of 
the brain, which can be seen in some of them, rising like the 
water in a fountain. There are six of these fontanelles. The 

Fia. 44. — The Skull, a, nasal bone; 6, superior maxillary ; c, inferior maxillary; 
d, occipital; e, temporal; /, parietal; g, frontal bone. 

anterior fontanelle is the largest, and is a lozenge-shaped space 
between the angles of the two parietal bones and the two 
segments of the frontal bone. The posterior fontanelle is 
much smaller in size, and is a triangular space between the 
occipital and two parietal bones. The other four fontanelles, 
two on each side of the skull, are placed at the inferior angles 
of the parietal bones : they are comparatively unimportant. 
The posterior fontanelle is closed by an extension of the ossify- 
ing process a few months after birth. The anterior remains 

Chap. IV.] THE SKELETON. 45 

open until the second year, and occasionally persists throagh- 
out life. The base of the skull is much thicker and stronger 
than the walls and roof ; it presents a 
number of openings for the passage of 
the cranial nerves, blood-vessels, etc. 

The diameters of the foetal skull 
given by King are : — 

Occipito-niental (from posterior fontanelle 

to chin) . . . . 5|- inches (140 mm.). 

Occipito-frontal (centre of frontal bone to 

occiput) .... 41 inches (114 mm.). 

Bi-parietal (from one parietal prominence ^,^ 45. -t1^ Skull at 

to another) . . 3^ inches (89 mm.). Birth. Superior surface. 1, 

posterior fontanelle ; 2, sagit- 
tal suture ; 4, anterior fon- 

The foetal cranial bones being iraper- taneiie; a, a, bi-parietal 

«., -n 1 ivi-i .T diameter; B, B, bi-temporal 

lectly ossmed, and their edges separated diameter. 

by membranous intervals, they are 

readily moulded, and they overlap one another more or less 

during parturition. 

The pelvic cavity. — The pelvis, so called from its resemblance 
to a basin, is stronger and more massively constructed than 
either the cranial or the thoracic cavity. It is composed of 
four bones, the ossa innominata, forming sides and front, and 
the sacrum and coccyx, completing it behind. It is divided 
by a brim or prominent line, the linea ilio-pectinea, into the 
false and true pelvis. The false pelvis is all that expanded 
portion of the pelvis situated above the brim : it forms an in- 
complete or " false " basin. The true pelvis is all that portion 
situated below the brim. Its cavity is a little wider in every 
direction than the brim itself, while the false pelvis is a great 
deal wider. The brim is, therefore, a narrowed bony ring or 
aperture between these two cavities; hence it is often termed 
the "strait"; while the space included within the strait or 
brim, is called the " inlet." The true bony pelvis is a basin 
with incomplete walls of bone and without a bottom to it: the 
opening below is called the "inferior strait" or "outlet." 

The female pelvis differs from that of the male in those 
particulars which render it better adapted to parturition, 
notably in being wider in every direction, which gives more 


room for the child to pass; in being shallower, which lessens 

Fig. 46. — Male Pelvis. 

the distance through which the child has to be propelled; and 
lastly, in the bones being thinner and smoother. 

Fig. 47. — Female Pelvis. 

Chap. IV.] THE SKELETON. 47 

The diameters of an average female pelvis given by King 
are : — 

Antero-posterior diameter of brim or inlet, 4 in. (102 mm.). 

Transverse diameter of brim or inlet . . 4 in. (102 mm.). 

Oblique dia:meter of brim or inlet . . . 4^ to 5 in. (114 to 127 mm.). 

Antero-posterior of outlet 41 to 5 in. (114 to 127 mm.). 

Transverse of outlet 4 in. (102 mm.). 

Oblique of outlet 4 in. (102 mm.). 












Superior maxillary. 


Inferior maxillary. 



Inferior turbinated. 


Os hyoides. 

7 cervical. 

12 dorsal. 


5 lumbar. 

5 sacral, or sacrum. 


. 4 coccygeal, 

or coccyx. 




Os innominatum. 









\ Scaphoid. 




Os calcis. 








Tarsus ■ 





Internal cuneiform. 


Os magnum. 


Middle cuneiform. 


^ Unciform. 

External cuneiform. 




es, or digits. 


3S, or digits. 



Fig. 48. — A Toothed, or 
Dentated Suture. 

The various bones of which the skeleton consists are con- 
nected together at different parts of their surfaces, and such 
connections are called joints or articulations. 

In all instances some softer substance is placed between the 
bones, uniting them together, or clothing the opposed surfaces ; 
but the manner in which the several pieces 
of the skeleton are thus connected varies 
to a great degree. We distinguish three 
varieties ; viz. those which are (1) immov- 
able, (2) slightly movable, (3) freely 

The immovable articulations. — The bones 
of the cranium and the facial bones (with 
the exception of the lower jaw) have 
their adjacent surfaces applied in close 

contact, with only a thin layer of fibrous tissue or of cartilage 
placed between their margins. In most of the cranial bones 

this union occurs by means of toothed 
ed^es which fit into one another and 
form jagged lines of union known as 
sutures. The suture between the fron^ 
tal and parietal bones is called the 
coronal suture; between the parietal 
and occipital, the larabdoidal; and be- 
LATioN. a, b, of fibro-car- twcen the two parietal bones, along the 
d!w.'' ''''''"'''' '''''"^^"'' middle line on the top of the crown, 

the sagittal suture. 
The slightly movable or mixed articulation. — In this form of 
articulation the bony suifaces are usually joined together by 


Fig. 49. — A Mixed Articu- 

Chap. V.] 



broad, flattened disks of fibro-cartilage, as in the articulations 
between the bodies of the vertebrse. These intervertebral 
disks being compressible and extensile, the spine can be moved 
to a limited extent in every direction. In the pelvis the articu- 
lation between the two pubic bones (symphysis pubis), and 
between the sacrum and ilia (sacro-iliac articulation), are also 
slightly movable. The pubic bones are united by a disk of 
fibro-cartilage and by ligaments. In the sacro-iliac articulation 
the sacrum is united more closely to the ilia, the articular sur- 
faces being covered by cartilage and held together by ligaments. 
The movable articulations. — This division includes the com- 
plete joints, — joints having a secreting membrane placed be- 
tween their opposing surfaces, which keeps them well lubricated 
and capable of free movement one upon the other. Each articular 
end of the bone is covered by cartilage, which provides surfaces 

of remarkable smoothness, and 
these surfaces are lubricated by 
the synovial fluid secreted from 
the delicate synovial membrane 
which lines the cavity of the 
joint. This membrane is contin- 
uous with the margin of the ar- 
ticular cartilage, and along with 
them completely encloses the 
joint cavity. The bones are 
united by fibrous connective 
tissue in tlie various forms of 
ligaments, such as membranous 
capsules, flat bands, or rounded cords. These ligaments are not 
always so tight as to maintain the bones in close contact in all 
positions of the joint, but are rather tightened in some positions 
and relaxed in others, so that in many cases they are to be looked 
upon chiefly as controllers of movements, and not as serving 
solely to hold the bones together. The bones are mainly held 
together in these joints by atmospheric pressure and by the 
surrounding muscles. 

The varieties of joints in this class have been determined 
by the kind of motion permitted in each. They are as 
follows : — 

(1) Gliding joint. Tlie articular surfaces are nearly flat, 


Fig. 50. — A Simple Complete Joint. 
The synovial membraue is represented 
by dotted lines. 


and admit of only a limited amount of gliding movement, 
as in the joints between the articular processes of the ver- 

(2) Hinge joint. The articular surfaces are of such shape 
as to permit of movement, to and fro, in one plane only, like a 
door on its hinges. These movements are called flexion and 
extension, and may be seen in the articulation of the arm with 
the forearm, in the ankle joint, and in the articulations of the 

(3) Ball and socket joint. In this form of joint a more or 
less rounded head is received into a cup-like cavity, as the head 
of the femur into the acetabulum, and the head of the humerus 
into the glenoid cavity of the scapula. Movement can take 
place freely in any direction, but the shallower the cup, the 
greater the extent of motion. 

(4) Pivot joints. In this form, one bone rotates around 
another which remains stationary, as in the articulation of the 
atlas with the axis, and in the articulation of the ulna and 
radius. In the articulation of the ulna and radius, the ulna 
remains stationary and the radius rotates freely around its 
upper end. The hand is attached to the lower end of the 
radius, and the radius, in rotating, carries the hand with it; 
thus, the palm of the hand is alternately turned forwards and 
backwards.^ When the palm is turned forwards, the attitude 
is called supination ; when backwards, pronation. 

(5) Ootid i/loid joints. When an oval-shaped head, or con- 
dyle, of a bone is received into an elliptical cavity, it is said to 
form a condyloid joint. An example of this kind of joint is 
found in the wrist. 

(6) Saddle joints. In this joint the articular surface of each 
bone is concave in one direction, and convex in another, at 
right angles to the former. A man seated in a saddle is 
"articulated" with the saddle by such a joint. For the saddle 
is concave from before backwards, and convex from side to 
side, while the man presents to it the concavity of his legs 
astride, from side to side, and the convexity of his seat, from 
before backwards. The metacarpal bone of tlie thumb is 
articulated with the wrist by a saddle joint. Both the con- 

1 Anatomists always speak of the body as being in the erect position, with 
the arms hanging, and the palms of the hands looking forwards. 

Chap. V.] JOINTS. 61 

dyloid and the saddle joints admit of motion in every direction 
except that of axial rotation. 

The different kinds of movement of which bones thus con- 
nected are capable, are — flexion and extension ; abduction and 
adduction ; rotation and circumduction. 

A limb is flexed, when it is bent; extended, when it is 
straightened out. It is abducted, when it is drawn away from 
the middle line of the body ; adducted, when it is brought 
to the middle line. It is rotated, when it is made to turn on 
its own axis ; circumducted, when it is made to describe a 
conical space, by rotation around an imaginary axis. No part 
of the body is capable of perfect rotation like a wheel, for the 
simple reason that such motion would necessarily tear asunder 
all the vessels, nerves, muscles, etc., which unite it with other 

As the synovial membranes are intimately connected with 
the joints, it may be well to give a brief description of them 

The synovial membranes are composed entirely of connective 
tissue, with the usual cells and fibres of that tissue. They are 
distinguished by the nature of their secretion, which is a viscid, 
glairy fluid, resembling the white of an egg and named synovia. 
From its nature, it is well adapted for diminishing friction, and 
thereby facilitating motion. 

These membranes are found surrounding and lubricating the 
cavities of the movable joints in which the opposed surfaces 
glide on each other ; in these situations they are called articu- 
lar synovial memhraiies. They are found forming sheaths for 
the tendons of some of the muscles, and thus facilitating their 
motion as they glide in the fibrous sheaths which bind them 
down against the bones ; they are here called vaginal synovial 
membranes^ or synovial sheaths. Lastly, they are found in the 
form of simple sacs, interposed, so as to prevent friction, be- 
tween two surfaces which move upon each other, and in these 
situations they take the name of bursal synovial membranes^ or 
synovial bursse. These bursse may be either deep seated or 
subcutaneous. The former are, for the most part, placed be- 
tween a muscle and a bone, or between a tendon and a bone. 
The subcutaneous bursse lie immediately under the skin, and 
occur in various parts of the body, interposed between the skin 



[Chap. V. 

and some firm prominence beneath it. The large bursa situ- 
ated over the pateUa is a well-known example of this class, 
but similar, though smaller, bursse are found also over the ole- 
cranon, the malleoli, the knuckles, and other prominent parts. 



Immovable Joint. 


r Sutura. — Articulations by processes and indentations 
interlocked together. A thin layer of fibrous tis- 
sue is interposed between the bones. Sutures may 
be dentated, tooth-like ; serrated, saw-like ; squa- 
mous, scale-like ; harmonic, smooth ; and grooved, 
for the reception of thin plates of bone. 


Slightly Movable 





Movable Joint. 

Symphysis. — The bones are united by a plate or 
disk of fibro-cartilage of considerable thickness. 

Syndosmosis. — The bony surfaces are united by 
an interosseous ligament, as in the lower tibio- 
fibular articulation. 

1. Arlhrodia. — Gliding joint; articulates by plane 
surfaces which glide upon each other. 

2. Ginglymus. — Hinge or angular joint ; moves back- 
wards and forwards in one plane. 

3. Enarthrosis. — Ball and socket joint ; articulates 
by a globular head in a cup-like cavity. 

4. Pivot. — Articulates by a pivot process turning 
within a ring, or by a ring turning round a pivot. 

5. Condyloid. — Ovoid head received into elliptical 

6. Reciprocal Reception. — Saddle joint; articular sur- 
faces are concavo-convex. 



Muscular tissue is the tissue by means of which the active 
movements of the body are produced. It is a more specialized 
kind of tissue than the connective, which, as we have seen, is 
used chiefly for mechanical purposes. Muscular tissue is irri- 
table, and if we irritate or stimulate it, it will respond. We 
may irritate or stimulate the bones, ligaments, or other connec- 
tive tissue structures and they will not 
respond, they will remain immovable ; if, 
however, we stimulate muscular tissue, 
it will show its response to the stimula- 
tion by contracting. This power of the 
muscle to contract is called muscular con- 
tractility. All muscular tissue consists 
of fibres, and whenever a muscle fibre con- 
tracts, it tends to bring its two ends, with 
whatever may he attached to them^ together. 
Influences which irritate or stimulate 
muscle fibres are spoken of under the 
general name of stimuli. 

Muscle fibres are of two different kinds, 
and we therefore distinguish two varieties 
of muscular tissue, the striped or striated, 

and the plain or non-striated. The striated muscle is nearly 
always under the control of the will, and is often spoken of as 
voluntary muscle ; the non-striated is usually withdrawn from 
the control of the will, and is often termed involuntary muscle. 

Voluntary, striated muscle is composed of long slender fibres 
measuring on an average about -^^ inch (.050 mm.) in diame- 


Fig. 51. — Diagram of 
Muscle Fibre with Sar- 
colemma attached. 



[Chap. VI. 

ter, but having a length of an inch or more. Each fibre con- 
sists of three distinct elements : (1) contractile substance, 
forming the centre and making up most of the bulk of the fibre ; 
(2) nuclei, which lie scattered upon the surface of the con- 
tractile substance; (3) the sarcolemma, a thin, structureless 

tube, which tightly en- 
closes the contractile sub- 
stance and the nuclei. 

If we examine a fresh 
muscle fibre microscopi- 
cally, we see that the 
contractile substance is 
marked with very fine in- 
distinct longitudinal lines, 
or stride; and in addition 

Fig. 52. -Fragments of Striped Fibres, ^q ^I^q longitudinal Stria- 
SHOwiNG A Cleavage in Opposite Direc- . . ° 

TiONS. (Magnified 300 diameters.) A, longitu- tion it is CroSSCd by more 

dinal cleavage; c, fibrillae separated from one ^ligti^ct narrow dark and 
another at the broken end of the fibre; c c , 

single fibrils more highly magnified, in c' the light bands or stripes,^ 
elementary structures are square, in c" round; • •■ ,. • -i,, n ,-, 

£, transverse cleavage; a, b, partially detached ^^^^ relative WKltn Ot tllC 

disks ; b' detaclied disk, more highly magnified, gtripes varying according 
showing the sarcous elements. ^ n^ • 

as the fibre is seen in a 
state of contraction or relaxation. The ultimate structure of 
muscular fibre is still by no means fully understood. This 
much, however, is certain, that the contractile substance is a 
complex chemical structure, and that the molecules of which it 
is composed readily change their places under the influence of 
certain stimuli. When a muscle contracts, the dark bands 
swell up and shorten (the light bands are also constricted), and 
the whole fibre broadens and shortens. This broadening and 
shortening is brought about by the molecules of each section 
of the fibre changing their places. We shall have a rough 
image of the movements of the molecules during a muscular 
contraction if we imagine a company of a hundred soldiers ten 
ranks deep, with ten men in each rank, rapidly, but by a series 
of gradations, extending laterally into a double line with fifty 
men in each line. 

1 By treating a fibre with certain chemical agents, we may cause it to break 
up longitudinally into fibrillse, and transversely into thin disks. Thus each fibre 
is resolvable into a number of tiny structures, which elementary structures have 
been termed sarcous elements. 

Chap. VI.] 



The striated muscles are all connected with nerves, and under 
normal conditions do not contract otherwise than by the agency of 
the nerves. They are also plentifully supplied with blood-vessels. 

The muscular fibres lie closely packed, their ends lapping 
over on to adjacent fibres, and forming bundles. These bundles 
are grouped so as to make 
larger bundles, and in this 
way the muscles which are 
attached to the skeleton are 

Involuntary, non-striated mus- 
cular tissue is composed of 
long, somewhat flattened, 
elongated fibre-cells. Each 
fibre-cell contains an oval or 
rod-shaped nucleus, contain- 
ing one or more nucleoli. 
The substance of the fibre- 
cell is longitudinally striated, 
but does not exhibit trans- 
verse striation. The fibre- 
cells lie side by side, or lap 
over one another at the ends, 
and are joined together by a 
small amount of cement sub- 

This kind of muscular tis- 
sue is found arranged around 
the blood-vessels and most 
of the hollow viscera. The 
fibres are variously grouped 
in different parts of the body ; 
sometimes crowded together 
in solid bundles, which are arranged in layers and surrounded 
by connective tissue, as in the intestines ; sometimes arranged 
in narrow interlacing bundles, as in the bladder ; sometimes 
wound in single or double layers around the blood-vessels ; and 
again, running in various directions and associated with bands 
of connective tissue, they form large compact masses, as in the 

Fig. 5'.>. — Wave of ('<intr action pass- 
ing OVER A Muscular Fibrk of Dytiscus. 
Very highly magnified. B, R, portions 
of the fibre at rest; C, contracted part; 
/, I, intermediate condition. 



[Chap. VI. 

Numerous nerves are supplied to non-striated muscular tissue, 
and many blood-vessels. 

The contraction of this kind of muscular tissue is much 
slower and lasts longer than the contrac- 
tion of the striated variety. As a general 
rule the muscles of the skeleton are thrown 
into contraction only by nervous impulses 
reaching them along their nerves ; sponta- 
neous contractions, as in a case of "cramps," 
being rare and abnormal. The plain mus- 
cular tissue of the internal organs, however, 
very often contracts indejiendently of the 
central nervous system, and under favor- 
able circumstances will continue to do so 
after the viscera have been removed from 
the body. 

The great increase in the muscular tissue of the 
uterus during gestation takes place both by elonga- 
tion and thickening of the pre-existing fibre-cells, 
Fig. 54.— Fibre-cells and also, it is thought, by the development of new 

OF Plain Muscular fibre-cells from small granular cells lying in the 
TissuK. Highly magni- ^ , , . , . , , ^ 

gg(j tissue. In the shrinking oi the uterus after par- 

turition the fibre-cells diminish to their previous 
size ; many of them become filled with fat granules, and eventually many 
are, doubtless, removed by al)sorption. 

Development of striated muscular tissue. — When the muscular fibres 
are about to be formed, the cells set apart for this purpose elongate, and 
their nuclei multiply, so that each cell is converted into a long, multi- 
nucleated protoplasmic fibre. At first the substance of the fibre is not 
striated, but presently it becomes longitudinally striated along one side, 
and about the same time a delicate membrane, the sarcolemma, may be 
discovered bounding the fibre ; then transverse striation commences, and 
gradually extends around the fibre, and, finally, the nuclei take up their 
position under the sarcolemma. 

Regeneration of muscular tissue. — It was formerly thought that after 
removal, by tlie knife, or by disease, muscular tissue was not regenerated, 
but that any breach of continuity which might occur in the muscle was filled 
up by a growth of connective tissue. It would appear, however, that the 
breach is after a certain lapse of time bridged across by muscular substance, 
but how the new muscular tissue is formed is not fully understood. 

Attachment of muscles to the skeleton. — The muscles are sepa- 
rate organs, each muscle having its own sheath of connective 
tissue. The connective tissue extends also into the muscle, form- 

Plate I. — Forms of Muscles and Tendons. A , adductor of thigh ; B, biceps of 
arm; L), deltoid; G, gastrocnemius; P , pronator of fore-arm; P", pectoral; R, 
rectus abdominis; R", rectus muscle of thigh; S', serratus magnus of thorax; S", 
semi-membranosus of thigh. 



ing sheaths for the smaller bundles, connecting and binding the 
fibres and bundles together, and conducting and supporting the 
blood-vessels and nerves distributed to the muscle fibres. 

The muscles vary greatly in shape and size. In the limbs 
they are of considerable length, forming more or less elongated 
straps ; in the trunk they are broad, flattened, and expanded, 
forming the walls of the cavities which they enclose. 

They are attached to the bones, cartilages, ligaments, and 
skin in various ways, the most common mode of attachment 
being by means of tendons. The muscular fibres converge as 
they approach their tendinous extremities, and gradually blend 
with the fibres of the tendons, the tendons in their turn insert- 
ing their fibres into the bones. Sometimes the muscles end in 
expanded form in the flat fibrous membranes, called aponeuroses. 
Again, in some cases, the muscles are connected with the bones, 
cartilages, and skin, without the intervention of tendons or 

In the description of muscles it is customary to speak of the 
attachments of their opposite ends under the names of origin 
and insertion, the first term origin being usually applied to the 
more fixed attachment ; the second term insertion being applied 
to the more movable attachment. The origin is, however, 
absolutely fixed in only a very small number of muscles, such 
as those of the face, which are attached by one end to the bone, 
and by the other to the movable skin. In the greater number, 
the muscle can be made to act from either end. 

The muscular tissue or flesh forms a large proportion of the 
weight of the whole body. The following has been calculated 
for a man of one hundred and fifty pounds' weight from the 
tables of Liebig: skeleton, twenty-eight pounds; muscles, sixty- 
two pounds ; viscera (with skin, fat, blood, etc.), sixty pounds. 

The total number of voluntary muscles may be stated at 
three hundred and eleven. It is not necessary for us to be able 
to distinguish more than a few of the most prominent. We 
may conveniently classify these into two groups : — 

1. Chief muscles of the head and trunk. 

2. Chief muscles of the limbs. 

Chief muscles of head, face, neck, and trunk. — The chief muscles 
of the head are the occipital and frontal muscles, which, united 

Plate II. — Muscles of Face, Head, and Neck. 1, sterno-cleido-mastoid; 
10, temporal ; 11, masseter ; 13, 13, occipito-f routalis. 




[Chap. VI. 

together by a thin aponeurosis extending over and covering 
the whole of the upper part of the cranium, are usually known 
as one muscle, the occipito-frontalis. The frontal portion of this 
muscle is the more powerful ; by its contraction the eyebrows 

are elevated, the skin of the forehead 
thrown into transverse wrinkles, and 
the scalp drawn forward. 

There are about thirty facial mus- 
cles; they are chiefly small, and con- 
trol the movements of the eye, nose, 
and mouth. 

The six muscles which move the 
Fig. 55. -Muscles of Right eyeball are the four straight or recti. 

Eyeball within the Orbit. 

Seen from the front. 21, superior and the twO Oblique, mUSCieS. ihc 

rectus ; 22, inferior rectus ; 23, ex- four recti have a common Origin at the 

terual rectus ; 24, internal rectus ; _ "^ _ 

25, superior oblique ; 26, inferior bottom of the Orbit ; they pasS straight 

°^^^*^"®' forwards to their insertion into the 

eyeball, one, the superior rectus, in the middle line above ; one, 
the inferior rectus, opposite it below, and one halfway on each 
side, the external and internal recti. The eyeball is completely 
imbedded in fat, and these mus- 
cles turn it as on a cushion, the 
superior rectus inclining the 
axis of the eye upwards, the in- 
ferior downwards, the external 
outwards, the internal inwards. 
The two oblique muscles are 
both attached on the outer side 
of the ball; their action is some- 
what complicated, but their 
general tendency is to roll the 
eyeball on its own axis, and pull 
it a little forward and inward. 

llie muscles of mastication are the masseter, the temporal, and 
tlie external and internal pterygoid. They all have their origin 
in the immovable bones of the skull, and are all inserted into 
the movable lower jaw. They generally act in concert, bring- 
ing the lower teeth forcibly into contact with the upper; they 
also move the lower jaw forward upon the upper, and in every 
direction necessary to the process of grinding the food. 

Fig. 56. — Muscles of Eyeball. Seen 
from side. 19, elevator muscle of eyelid ; 
22-26, same as in Ficr. 55. 

Chap. VI.] 



Fig. 57. — Muscles of the Tongue. 

The chief muscles connecting the tongue and tongue bone to 
the lower jaw are the genio-glossus and stylo-g^lossus. They are 
interesting to us from the fact that during general anaesthesia 
they, together with the other muscles, become relaxed, and it 
is necessary to press the angle 
of the lower jaw upwards and 
forwards in order to prevent 
the tongue from falling back- 
wards and obstructing the 

The most prominent muscle 
of the neck is the sterno-cleido- 
mastoid. It is named from its 
origin and insertion, arising 
from part of the sternum and 
clavicle, and being inserted 
into the mastoid portion of the 
temporal bone. This muscle 
is easily recognized in thin 
persons by its forming a cord- 
like prominence obliquely situated along each side of the neck. 
It serves as a convenient landmark in locating the great vessels 
carrying the blood to and from the head. If one of these 
muscles be either abnormally contracted or paralyzed, we get 
the deformity called wry neck. 

The muscles of the trunk may be arranged in three groups : 
(1) muscles of the back; (2) muscles of the thorax; (3) muscles 
of the abdomen. 

The muscles of the back are disposed in five layers, one be- 
neath another. The two largest and most superficial are the 
trapezius and tlie latissimus dorsi. 

The trapezius arises from the middle of the occipital bone, 
from the ligamenfum nuchce, and from the spinous processes of 
the last cervical and all the dorsal vertebrae. From this ex- 
tended line of origin the fibres converge to their insertion in 
the acromion process and spine of the scapula. The latissimus 
dorsi arises from the last six dorsal vertebrae, and through the 
medium of the lumbar aponeurosis, from the lumbar and sacral 
part of the spine and from the crest of the ilium. The fibres 
pass upwards and converge into a thick, narrow band, which 


winds around and finally terminates in a flat tendon, which is 
inserted into the front of the humerus just below its head. 

These muscles cover nearly the whole of the back; but as they 
act upon the bones of the upper extremity, they are often more 
properly reckoned as belonging to the muscles of that region. 

The muscles of the thorax are chiefly concerned with the 
movements of the ribs during respiration. They are the inter- 
costals, subcostals, etc. 

The chief bulk of the anterior muscular wall of the chest is 
made up of the pectoral muscles, the larger of which arises partly 
from the front of the sternum. The fibres converging form 
a thick mass, which is inserted by a tendon of considerable 
breadth into the upper part of the humerus. As these muscles 
move the arm, they are, like the superficial muscles of the back, 
usually reckoned among the muscles of the upper extremity. 
Covering the pectoral muscles is a superficial fascia (composed 
of connective tissue) in which are lodged the mammary glands 
and a variable amount of fat. 

The muscular walls of the abdomen are mainly formed by 
three layers of muscles, the fibres of which run in different 
directions, those of the superficial and middle layers being 
oblique, and those of the innermost layer being transverse. In 
the front of the abdomen these three layers of muscles are 
replaced by tendinous expansions or aponeuroses, which meet in 
the middle line, the line of union giving rise to a white cord- 
like line, the linea alba. On each side of this line the fibres of 
a straight muscle, the rectus muscle, extend in a vertical direc- 
tion between the tendinous layers. The abdominal muscles 
are covered and lined by sheets of fascise, some of which are 
very dense and strong, and serve to strengthen weak points in 
the muscular walls. 

The strongest and most superficial of the abdominal muscles 
is the external oblique, the fibres of which, arising from the lower 
eight ribs, incline downwards and forwards and terminate in the 
broad aponeurosis, which, meeting its fellow of the opposite side 
in the linea alba, covers the whole of the front of the abdomen. 
The lowest fibres of the aponeurosis are gathered together in 
the shape of a thickened band, which extends from the anterior 
superior spinous process of the ilium to the pubic bone, and 
forms the well-known and important landmark, called from the 

Pi»A.TE III,— Muscles of Back. 50, latissimus dorsi ; 51, trapezius ; 52, deltoid 



anatomist who first described it, Poupart's ligament. Just 
above this ligament, and near the pubic bone, is an oblique 
opening which transmits the spermatic cord in the male, or the 
round ligament in the female. This opening, called the ex- 
ternal abdominal ring, is usually the seat of hernia. 

The internal oblique muscle lies just beneath the external 
oblique. Its fibres run upwards and forwards, and end for the 
most part in a broad aponeurosis. At the outer border of the 
rectus muscle this aponeurosis divides into two layers, one passing 
before, the other behind, that muscle: they reunite at its inner 
border in the linea alba, and thus form a sheath for the rectus. 

The transversalis muscle lies beneath the internal oblique; 
the greater part of its fibres have a horizontal direction, and 
extend forward to a broad aponeurosis in front. 

The rectus is a long, flat muscle, consisting of vertical fibres 
situated at the fore part of the abdomen, and enclosed in the 
fibrous sheath formed by the aponeurosis of the internal oblique. 
It arises from the pubic bone, and is inserted into the cartilages 
of the fifth, sixth, and seventh ribs; it is separated from the 
muscle of the other side by a narrow interval which is occupied 
by the linea alba. 

The linea alba, or white line, is a tendinous band formed by 
the union of the aponeuroses of the two oblique and transverse 
muscles, the tendinous fibres crossing one another from side to 
side. It extends perpendicularly, in the middle line, from the 
ensiform portion of the sternum to the pubis. It is a little 
broader above than below, and a little below the middle it is 
widened into a flat circular space, in the centre of which is sit- 
uated the cicatrix of the umbilicus. 

The abdominal muscles perform a threefold action. When 
acting from both pelvis and thorax as fixed points they com- 
press the abdominal viscera by constricting the cavity of the 
abdomen, in which action they are much assisted by the descent 
of the diaphragm. (See below.) By these means they give 
assistance in expelling the foetus from the uterus, the faeces 
from the rectum, tlie urine from the bladder, and its contents 
from the stomach in vomiting. When the pelvis and spine are 
the fixed points the abdominal muscles raise the diaphragm by 
pressing on the abdominal viscera, draw down the ribs, compress 
the lower part of the thorax, and assist in expiration. Again, 

Plate IV. - Muscles of Chest and Ahdomen. 55, pectoral muscle • 44 sermtus 
magnus ; M, external oblique ; :^5, rectus abdo.uinis, the external layer of ap^neuiot^ 
sheath IS removed : 38, linea alba ; 40, aponeurosis. aponeurotic 



if the trunk and arms are the fixed point, the muscles draw the 
pelvis upwards as a preparatory step to the elevation of the 
lower limbs in the action of climbing. 

The diaphragm is a thin musculo-fibrous partition, placed 
obliquely between the abdominal and tb.oracic cavities. It is 
fan-shaped, and consists of muscle fibres arising from the whole 
of the internal circumference of the thorax, and of an aponeu- 
rotic tendon, shaped somewhat like a trefoil leaf, into which 
the muscle fibres are inserted. (^Vide Plate V, page 121, for 
illustration of diaphragm.) It has three large openings for 
the passage of the aorta, the large artery of the body, the in- 
ferior vena cava, one of the largest veins of the body, and the 
oesophagus or gullet ; it has also some smaller o^^enings, of 
less importance, for the passage of blood-vessels, nerves, etc. 
The upper or thoracic surface of the diaphragm is highly 
arched ; the heart is supported by the central tendinous por- 
tion of the arch, the right and left lungs by the lateral portions, 
the right portion of the arch being slightly higher on the right 
than on the left side. The lower or under surface of the dia- 
phragm is deeply concave, and covers the liver, stomach, pan- 
creas, spleen, and kidneys. 

The action of the diaphragm modifies considerably the size 
of the chest, and the position of the thoracic and abdominal 
viscera, and it is essentially the great respiratory muscle of the 
body. The mechanical act of respiration consists of two sets 
of movements; viz. those of inspiration and of expiration, in 
which air is successively drawn into the lungs and expelled 
from them by the alternate increase and diminution of the 
thoracic cavity. The changes in the capacity of the thorax are 
efifected by the expansion and contraction of its lateral walls, 
called costal respiration, and by the depression and elevation 
of the floor of the cavity, through contraction and relaxation 
of the diaphragm, called diaphragmatic or abdominal respiration. 
These two movements are normally combined in the act of 
respiration, but in different circumstances one of them may be 
employed more than the other. Abdominal respiration pre- 
dominates in men and in children, and costal respiration in 
women.i jj^ ^l^g o^^^ of inspiration the diaphragm contracts, 

1 The costal respiration of women is abnormal, and has been shown to be 
due to their mode of dress. 

Chap. VI.] 



and in contracting flattens out and descends, the abdominal 
viscera are pressed downwards, and the thorax is expanded 
vertically. In normal and quiet expiration the diminution of 
the capacity of the chest is 
mainly due to the return of 
the walls of the chest to the 
condition of rest, in conse- 
quence of their own elastic 
reaction, and of the elasticity 
and weight of the viscera dis- 
placed by inspiration. In more 
forcible acts of expiration, and 
in efforts of expulsion from the 
thoracic and abdominal cavi- 
ties, all the muscles which tend 
to depress the ribs, and those 
which compress the abdominal 
cavity, concur in powerful ac- 
tion to empty the lungs, to fix 
the trunk, and to expel the con- 
tents of the abdominal viscera. 
Thus the diaphragm is an ex- 
pulsive as well as the chief 
respiratory muscle of the body. 
Muscles of the upper extrem- 
ity. — A certain number of 
muscles situated superficially 
on the trunk pass to the bones 
of the shoulder and of the 
arm, so as to attach the upper 
limbs to the trunk. Of these, 
the two superficial muscles we 
have mentioned as covering the 
back, the trapezius and latis- 
simus dorsi, and the pectoral 
muscles covering the front of Fig. 58. — Muscles of Arm. 58, biceps; 

KQ tl'icGDS 

the chest, are the chief. The 

most prominent muscles found in the upper limbs are : — 

Deltoid. Triceps. Supinators. Extensors. 

Biceps. Pronators. Flexors. 



[Chap. VI. 

The deltoid is a coarse triangu- 
larmuscle which gives the rounded 
outline to the shoulder; it extends 
downwards and is inserted into 
the middle of the sliaft of tlie 
humerus. It raises the arm from 
the side so as to bring it at right 
angles to the trunk. 

The biceps is a long fusiform 
muscle, occupying the whole of 
the anterior surface of the arm; 
it is divided above into two por- 
tions or heads, from which cir- 
cumstance it has received its 
name. It arises by these two 
heads from the scapula, and is 
inserted into the radius. It flexes 
and supinates the forearm on the 

The triceps is situated on the 
back of the arm, extending the 
whole length of the posterior sur- 
face of the humerus. It is of 
large size, and divided above into 
three heads; hence its name. It 
is inserted into the ulna. It is 
the great extensor muscle of the 
forearm, and is the direct antago- 
nist of the biceps. 

The muscles covering the fore- 
arm are disposed in groups, the 
pronators and flexors being placed 
on the front and inner part of the 
forearm, and the supinators and 
extensors on the outer side and 
back of the forearm: they antag- 
onize one another. The prona- 
FiG. 59. — Muscles in Fnofir of i r i i j 

Forearm. (52, pronator teres ; 63, (55, torS turn the palm ot the hand 

^^ I'!' i'^^^^'"!' 70, .supinator lonsus; fo^vvards, and, when the elbow 

71, 77, 78, extensors; a, annular liga- ' 

ment. is flexed, downwards or prone. 

Chap. VI.] THE MUSCLES. 69 

The supinators turn the palm of the hand backwards, and, 
when the elbow is flexed, upwards or into the supine position. 
Tire flexors and extensors have long tendons, some of which 
are inserted into the bones of the wrist, and some into the bones 
of the fingers: they serve to flex and extend the wrist and 

Muscles of the lower extremity. — These include the muscles 
of hip, thigh, leg, and foot. The most important of these are : — 

Glutei or gluteal muscles. Tibialis anticus. Soleus. 

Posterior femoral. Extensors. Flexors. 

Anterior femoral. Peroneal. Tibialis posticus. 

Internal femoral. Gastrocnemius. 

If we compare the muscles of the shoulder and arm with 
those of the hip and leg, we shall see that the anterior muscles 
of the former correspond roughly with the posterior muscles 
of the latter, the muscles of the hip and leg, however, being 
larger and coarser in texture than those of the shoulder and 

The glutei, or three gluteal muscles, form the chief prominence 
of the buttock. They are coarse in texture, and are largely 
concerned in supporting the trunk upon the head of the femur, 
and in bringing the body into the erect position when the 
trunk is bent forwards upon the thigh. 

The posterior femoral or hamstring muscles cover the back of 
the thigh. There are three of these muscles, — the biceps, the 
semitendinosus, and the semimembranosus. The chief of these 
is the biceps, and is somewhat analogous to the biceps covering 
the front of the arm. The action of the hamstring muscles is 
to flex the knee and to extend the hip. 

The principal anterior femoral muscles are the quadriceps and 
sartorius. The quadriceps covers the front of the thigh, and 
is analogous to the triceps covering the back of the arm; it is 
the great extensor of the leg; it also flexes the hip, and antago- 
nizes the action of the hamstring muscles. The sartorius, or 
tailor's muscle, is a long, ribbon-like muscle, the longest in the 
body: it crosses the thigh obliquely from its origin in the ilium 
to its insertion in the tibia. It was formerly supposed to be 
the muscle principally concerned in producing the posture 
assumed by the tailor in sitting cross-legged, and hence its name. 

Fig. go. — Muscles of thb 
Thigh. 46, gluteus maximus; 
36, 35, posterior femoral; 33, sar- 
torius; 27, 26, internal femoral 
or adductor. 

I iT' »'| 

Fig. 61. — Muscles of Leg. 
Superficial View of the 
Calf. 22, tendo Aehillis : 21, 
gastrocnemius ; 18, soleus ; 16, 
peroneal muscles. 

Chap. VI.] THE MUSCLES. 71 

The internal femoral or adductor muscles occupy the internal 
portion of the thigh: they are all adductors of the thigh. 

The tibialis anticus, the extensors, and the peroneal muscles 
cover the front and outer side of the leg. The gastrocnemius 
and the soleus, the flexors, and the tibialis posticus cover the 
back of the leg. The action of the tibialis anticus and of one 
of the three peroneal muscles is to Ilex the ankle, while the 
action of the tibialis posticus and the other peroneal muscles is 
to extend the ankle. The flexors and extensors act on the toes. 

The gastrocnemius and soleus form the calf of the leg ; they 
are inserted into a common tendon, the tendo Achillis, which 
is the thickest and strongest tendon in the body, and is inserted 
into the os calcis, or heel bone. The muscles of the calf possess 
considerable power, and are constantly called into use in stand- 
ing, walking, dancing, and leaping; hence the large size they 
usually present. 

The sole of the foot is protected by a fascia, called the plantar 
fascia, which is very strong, and the densest of all the fibrous 

Most of the muscles are covered closely by sheets of fibrous 
connective tissue (fascice), and this deep layer of tissue forms a 
nearly continuous covering beneath the superficial or subcu- 
taneous layer of areolar connective tissue, which in a former 
chapter we saw to be continuous over the whole of the body. 
Parts of the deep fasciae in the vicinity 
of the larger joints, as at the wrist and 
ankle, become blended into tight trans- Mz'. 

verse bands which serve to hold the 
tendons close to the bones, and receive 
the name of annular ligaments. ^^^^W-- ; j 

Relation of muscles to nerves. — The 
function of the muscles is to contract \\^ 

so that their two ends are drawn to- ^r^ \ ] 

gether, and a movement is thus pro- J^^^^^^~-['l 

duced which by various systems of ^^^^Ssirr 

levers can be converted into the par- fig. 62. — Nerve ending in 
ticular form of motion required. For ^iZlT ^Zi;^::.^^^^. 

example, the contraction of the mUS- torial ending of the axone, IS 

cles of the calf draws the heel upward, ^^^^ ^' eways. 

and in this way causes the whole body to be elevated on the toes. 



[Chap. VI. 

Ill order to bring about a muscular contraction the muscle 
must be stimulated. The way in which a muscle is normally 
stimulated is through its nerve, which conducts the nerve 
impulses from the central nervous system to the muscle fibres. 
Arriving at the latter, the nerve impulses bring about the 
complex chemical changes upon which the contraction of the 
muscle depends. When the nerve impulses cease, the muscle 
relaxes again. 


Occipito-frontalis. Head. 

Temporal, i l 

Masseter. 1- Muscles of Mastication. 

Pterygoids. J 

Exterior rectus. 

Interior rectus. I ;■ Face. 

Superior rectus. 

Inferior rectus. 

Superior oblique. | 

Inferior oblique. J 

Genio-glossus. 1 
Stylo-glossus. J 

Stern o-cleido-mastoid. 
Intercostals. 1 

Subcostals. I 

Levatores costarum. \ Thorax. 
Pectoral major. I 

Pectoral minor. J 

Diaphragm. Between Thorax and Abdomen. 

Obliquus externus abdominis. 1 


}■ Muscles of the Eye. 



Obliquus internus abdominis. 
Transversalis abdominis. 
Rectus abdominis. 
Trapezius. | ^^^^ 

Latissimus dorsi. j 

Deltoid. Shoulder. 

> Abdomen. 


Biceps flexor cubiti. | 
Triceps extensor cubiti. J 

Pronators (2). 

Supinators (2). 

Flexors of the wrist (2). 

Flexors of fingers and thumb (3) 

Extensors of wrist (3). 

Extensors of fingers and thumbs (6). 


Chap. VI.] 



r Maximus. i 
Glutei -1 Medius. 1- Hip. 
I Minimus. J 

Posterior femoral 

Anterior femoral 

Internal femoral 

( Biceps flexor cruris. 

j Semitendinosus. 

I- Semimembranosus. 

[ Quadriceps extensor cruris. 

[ Sartorius. 

I xVdductor longus. 

J, Adductor brevis. 


I Adductor magnus. 


Tibialis anticus. 

Tibialis posticus. 

Peroneal (3). 



Flexors of toes (4). 

Extensors of toes (4). 




The neurone. — Just as the anatomical and physiological unit 

of the muscular tissue is the muscle-cell, or as it is often called, 
the muscle-fibre, so the unit of the ner- 
vous system is the nerve-cell, or neurone. 
Thus the structure of the nervous system 
depends upon the position and relations 
of the neurones which compose it; and 
the activity of this system as a whole is 
the sum of the activities of its neurones. 

Although the neurones or nerve-cells 
vary considerably in size and in form, 
there are certain structural characteristics 
which they all possess in common. The 
typical neurone consists of a small mass 
of granular cytoplasm which surrounds 
a large vesicular nucleus. From this 
cytoplasm arise processes of varying 
length and form. The latter are of two 
kinds. Usually in the first variety (den- 
drones) the cytoplasm is granular and 
closely resembles that surrounding the 
nucleus ; they are usually short, and soon 
after their origin break up into numerous 
branches. In the second variety (axones) 
the processes are not granular, but show 

fine longitudinal striations ; they are often of great length and 

branch only near their termination. 

The nucleus, together with the cytoplasm surrounding it, is 

often called the " cell-body," so we may regard the neurone, or 


Fig. 63. — Diagram of 
A Neurone. A, axone 
arising from the cell-body 
and branching at its ter- 
mination ; D, dendrones ; 
C and N, cell-body com- 
posed of C, cytoplasm, and 
N, nucleus. 


nerve-cell, as being made up of a cell-body and its processes. 
Inasmuch as the processes arise from the cell-body, the latter 
is often spoken of as the " origin " of the fibres. By the origin 
of a fibre, then, we mean the cell-body from which that fibre 

Like the muscle-cell the neurone is irritable and responds to 
stimuli, but its mode of response is quite different from that of 
the muscle. If a muscle be stimulated, changes occur in its sub- 
stance, which changes result in the contraction of the muscle. 
If, however, we stimulate a neurone, we find that although there 
is no visible alteration in the part stimulated, yet a change in 
the substance of the neurone takes place which passes along 
throughout the entire neurone, and even to adjacent neurones, 
and so on from neurone to neurone often for a great distance. 
This invisible change which sweeps like a wave along the 
neurone is called the " nerve-impulse " ; and the fundameyital 
property of the neurone is to conduct nerve-impulses. 

We may roughly compare the passage of a nerve-impulse along 
a neurone with the passage of the electrical current along a wire. 

The result of the stimulus depends not upon any peculiarity 
of the neurone itself, but upon its anatomical relations to other 
neurones, and to other tissues of the body. Thus, if impulses 
be conducted to a muscle-fibre, the muscle contracts ; but if 
they be conducted to the brain, we have as the result a con- 
scious sensation. 

Under normal conditions an impulse always passes along a 
neurone in the same direction, travelling towards the cell-body 
by the dendrones, and away from it by the axones. Hence the 
dendrones may be regarded as receiving processes ; the axones 
as transmitting processes. 

The nervous system of man and of the higher animals has 
been divided into the following parts : — 



Tap a J ^P^°^^ \ Peripheral Nervous System. 

1 Sympathetic J 

Spinal Cord i 

C Medulla oblongata I Cerebro- spinal Axis, 

■o I Pons Varolii v or 

] Cerebellum I Central Nervous System. 

I Cerebrum j 



[Chap. VII. 

Nerves. — Nerves, or as they are sometimes called, nerve- 
trunks, are whitish cords which arise from the cerebro-spinal 
axis, and, branching as they go, are distributed to all parts of 
the body. Every organ and tissue has thus its supply of nerves 
connecting it with the brain or spinal cord (Fig. 64). 

If we examine a nerve 
under the microscope, we 
find that it is composed 
of nerve-fibres, each fibre 
being composed of an 
axone enclosed in a sheath. 
These fibres are of two 
kinds, the medullated and 
the non -medullated. The 
former consists of a central 
core, — the axone, — sur- 
rounded by a thick sheath 
of white fatty substance 
forming what is known 
as the medullary sheath. 
Surrounding this is a 
second sheath, the neuri- 
lemma, which is very deli- 
cate and has numerous 
nuclei situated along its 
innersurface. The second 
variety of nerve-fibres 
(the non-medullated) 
have a similar structure 
except that in them the 
medidlary sheath is ab- 

Between the nerve- 
fibres is a small amount 
of connective tissue which 
serves not only to bind the fibres together into bundles, or 
funiculi^ but also to carry to or from the fibres the blood- 
vessels and the lymphatics necessary for their nutrition. 

1 In the white matter of the brain and spinal cord the fibres are without a 
neurilemma, and in the gray matter the medullary sheath is also lacking. 

Fig. 64. — Diagram illustrating the Gen- 
eral Arrangement of the Cerebro-spinal 


Chap. VII.] 



Connective tissue also surrounds these bundles in the form of a 
sheath. The smaller nerves may consist of a single funiculus; 
but the larger nerve-trunks contain several funiculi united by 
connective tissue and surrounded by a common sheath of the 
same material. 

Although the nerves branch frequently throughout their 
course, and these branches often meet and fuse with one 
another, or with the branches of other nerves, yet each nerve- 
fibre always remains quite distinct, never branching until it 
reaches its termination, and never uniting with other nerve- 
fibres. The nerve-trunk is thus merely an association of indi- 
vidual fibres which proceed together towards the periphery. 
At any time one or more indi- 
vidual fibres may leave the 
main body and pass to their 
terminations, or may join an- 
other nerve; but in any case 
each fibre always remains per- 
fectly distinct. 

Physiologically speaking, 
nerve-fibres are of two kinds, Fig. <;5. — NERVE-FiBKiLs. «. ncrve- 

. 1 • 1 n • fibre, showing complete interruption of 

those which normally transmit the white substance ; b, another norve- 

impulses from the central ner- ^^'''' ^'^^"^ nucleus, in both these nerve- 

^ . fibres the white substance is stained black 

VOUS system to the periphery with osmic acid, and the axoue is seen run- 

(the effereyit or mo^or fibres), "ing as an uninterrupted strand through 

^ JJ ^' the centre of fibre, c, ordinary nerve- 

and those which normally fibre unstained ; d, e, smaller nerve-fibre; 

, -i • 1 • .1 /■, varicose nerve-fibre ; «, non-medullated 

transmit impulses m the re- nerve-fibres. 

verse direction (the afferent or 

sensory fibres). Hence nerves are spoken of as motor, sensory, 

or mixed ; according as they contain motor (efferent), sensory 

(afferent), or both kinds of fibres. 

The cell-bodies, from which the axones of the peripheral 
nerve-fibres arise, are not scattered promiscuously throughout 
the body, but are gathered together in certain definite regions 
or groups. These form the gray matter of the cerebro-spinal 
axis and the ganglia. 

The ganglia. — A ganglion is a small collection of cell-bodies 
connected by means of nerve-fibres (axones or dendrones) with 
other ganglia, and with the central nervous system. The 
ganglia may be divided into two large classes, the spinal and 



[Chap. VIL 

the sympathetic ganglia. ^ (The spinal ganglia will be con- 
sidered later.) 

The sympathetic system. — The sympathetic system consists of 
a double chain of ganglia, placed on each side of the spinal 
column, and united to each other by longitudinal filaments. 
The fibres that arise from them are mostly of the non-medul- 
lated variety. 

Fig. 66. — Section of the Internal Saphenous Nerve. Stained in osmic 
acid and subsequently hardened in alcoliul. Drawn as seen under a very low magni- 
fying power. (G. A. S.) ep, epineurium, or general sheath of the nerve, consisting 
of connective tissue separated by cleft-like areolis, which appear as a network of 
clear lines, with here and there fat-cells,/, /, and blood-vessels, v :, per, perineurium, 
or particular sheath of funiculus ; end, endoneuriuni, or connective tissue within 
funiculus, embedded in which are seen the cut ends of the medullated nerve-fibres. 
The fat-cells and the nerve-fibres are darkly stained by the osmic acid. 

These ganglia and nerves do not form an independent ner- 
vous system, for each ganglion is connected by motor and sen- 
sory fibres with the cerebral system. The sympathetic nerves 
are distributed to the viscera and blood-vessels, of which the 
movements are involuntary, and the general sensibility obtuse. 
They form networks or plexuses upon the heart, about the 

1 Isolated ganglia are also found in the course of some of the cranial nerves, 
and in some of the organs of special sense. 

Chap. VII.] 



stomach, and other viscera in the trunk ; they also enter the 
cranium, send branches to the organs of special sense, and, 
in particular, influence 
the pupil of the eye. 
Their most important 
distribution, however, 
is in connection with 
the blood-vessels. 
They form plexuses 
around the vessels, 
especially the arteries, 
and send fibres to ter- 
minate in the involun- 
tary muscular tissue 
of which the walls of 
these tubes are largely 
composed. The nerves 
thus distributed are 
called " vaso-motor " 

In the sympathetic 
ganglia the relation of 
the neurones is such 
that each nerve-fibre, 
arriving at the gan- 
glion from the spinal 
cord, is brought into 
contact with several 
other neurones which 
lie wholly in the sym- 
pathetic system. Thus 
an efferent impulse, 
passing along an axone 
from the cord, may 
pass to the dendrones 
of several sympathetic 
cells, and then by their Fig. 67. — General View of the Sympathetic 

axonps to thp -smnrifli System. 1, 2, 3, cervical ganglia ; 4, 1st thoracic 
axones to ine smootn ganglion; 5, Ist lumbar ganglion; 6, 7, sacral gan- 
muscles of the viscera, glion ; 9, 9, cardiac nerves ; 13, branch of pneumo- 
, • •! T gastric nerve ending in seini-lunar ganglion; 14, 

or to sinnlar endings, epigastric plexus. 



[Chap. VII. 

As a result the impulse is distributed over an area supplied by 
several sympathetic neurones. Similarly, sensory impulses, 
originating in any part of the area supplied by a particular 
group of sympathetic neurones, may be transmitted to a single 
afferent dendrone which connects with the axones of several 
sympathetic cells. These relations can best be understood by 
studying the accompanying diagram (Fig. 68). 

The spinal cord and spinal nerves. — The spinal cord is a 
column of gray and white soft substance, extending from the 
top of the spinal canal, where it is continuous with the brain, to 
about the second lumbar vertebra, where it tapers off into a fine 

thread. Before its 
termination it gives 
off a number of 
fibres which form a 
tail-like expansion, 
called the eaiida 

Like the brain, 
the spinal cord is 
protected and nour- 
ished by three 
membranes. These 
membranes have 
tlie same names and 
practically exercise 
the same functions 
as those enveloping 
the brain (for description of which see page 85). Tlie outer 
membrane is not attached to the walls of the spinal canal, being 
separated from them by a certain quantity of areolar and 
adipose tissue, and a network of veins. Therefore, the spinal 
cord does not fit closely into the spinal canal, as the brain does 
in the cranial cavity, but is, as it were, suspended within it. 
It diminishes slightly in size from above downwards, with the 
exception of presenting two enlargements in the cervical and 
dorsal regions, where the nerves are given off to the arms and 
legs respectively. It is usually from sixteen to seventeen 
inches (406 to 432 mm.) long, and has an average diameter of 
three-fourths of an inch (10 mm.). The spinal cord is almost 

Fig. 68. — Diagram showing the Relation of 

RONES. A, a medullated fibre, axone, or dendrone, 
coming from cerebro-spinal system and dividing into 
numerous branches on reaching a sympathetic ganglion. 
These branches connect with those of the cells, B, B, in 
the ganglion, and these cells send their non-meduUated 
fibres, axones, or deudrones, to supply the viscera, 
C, C, C, C. 

Chap. VIL] 



completely divided into lateral 
halves by an anterior and pos- 
terior fissure, the anterior fis- 
sure dividing it in the middle 
line in front, and the posterior 
fissure, in the middle line be- 
hind. In consequence of the 
presence of these fissures, only 
a narrow bridge of the sub- 
stance of the cord connects its 
two halves, and this bridge is 
traversed throughout its en- 
tire length by a minute central 
canal, — the canalis centralis. 
On making a transverse section 
of the spinal cord, the gray 
matter is seen to be arranged 
in each half in the form of a 
half-moon or crescent, with one 
end bigger than the other, and 
with the concave side turned 
outwards. The convex sides of 
the gray matter in each half 
approach one another, and are 
joined by the isthmus or bridge 
which contains the central 
canal. The tips of each cres- 
cent are called its horns or 
cornua, the front or ventral 
horns being thicker and larger 
than the dorsal. The white 
matter of the cord is arranged 
around and between the gray 
matter, the proportion of gray 
and white matter varying in 
different regions of the cord. 
The white matter, as in the 
brain, is composed of medul- 
lated nerves, and the gray 
matter of cell-bodies and fine 


Fig. 69. — Base of Brain, Spinal 
Cord, and Spinal Nerves. — V, 5th 
nerve ; VI, 6th nerve ; VII, a, facial nerve, 
b, auditory nerve; VlII, piieunio-gastric 
nerve ; VIII, a, glosso-pharyngeal, b, 
spinal accessory ; IX, hypoglossal ; c^^c', 
cervical nerve roots ; D^D^'^, dorsal nerve 
roots ; U—Ip, lumbar nerve roots; S^, S^, 
4th and 5th sacral nerves ; C'occ, coccyg- 
eal nerves; i?. P., brachial plexus; L.P., 
lumbar plexus ; S. P., sacral plexus; Sa, 
b, c, cervical sympathetic ganglia. 



[Chap. VII. 

gray fibres (naked axones and dendrones), all held together 
and supported by delicate connective tissue. The majority 
of the raedullated fibres run in a longitudinal direction. There 
is no real division between the brain and spinal cord, the brain 
being built upon the cord, and together they form the great 

Fia. 70. — Transverse Sections of the Spinal Cord at Different Levels. 
(Gowers.) (Twice the natural size.) 

nerve-centre or axis — the cerebro-spinal — which, by means 
of the cranial and spinal nerves, is placed in connection with all 
parts of the body. 

The spinal nerves. — There are thirty-one pairs of spinal 
nerves, arranged in the following groups, and named from 
the regions through which they pass. They are : — 

Chap. VII.] 








6 pairs 
12 " 
5 " 
5 " 

1 pair 


The spinal nerves pass out of the spinal canal through the 
intervertebral foramina, the openings between the vertebroe 
spoken of in the lesson on the bones of the spine. 

Each spinal nerve has two roots, a ventral root and a dorsal 
root. The fibres connected with these two roots are collected 
into one bundle, and 
form one nerve just — ■ ^ '^ 

before leaving the canal 
through the interverte- 
bral openings. Before 
joining to form a com- 
mon trunk, the fibres 
connected with the dorsal 
root present an enlarge- 
ment, this enlargement 
being due to a ganglion, 
or small nerve-centre. 
The fibres of the ventral 
root arise from the gray 
matter in the ventral 
horn, and are direct pro- 
longations from the cell- 
bodies there. The fibres 
of the dorsal root, on the other hand, arise from the cell-bodies 
in the ganglion, and ^row into the nerve-centres forming the gray 
matter in the dorsal horn. All the fibres growing from the ven- 
tral root are efferent fibres, and convey nervous impulses from 
the spinal cord to the periphery. The fibres growing into the 
dorsal root are afferent fibres, and convey nervous impulses from 
the periphery to the spinal cord. 

It should be borne in mind that the dorsal roots contain only 
sensory fibres, and that these fibres always have their origin 
outside of the cord (i,.e. in the spinal ganglia), while the ventral 
roots contain only motor fibres, and these have their origin 
within the central nervous system. This is true also of the 

Fig. 71. — Diagram showing Anatomy of 
THE Spinal Nerve Roots and Adjacent 
Parts. G., gray matter of the spinal cord; W., 
white matter of the same; D.H., dorsal horn of 
gray matter; F.//., ventral horn of gray matter ; 
D.R., dorsal root of spinal nerve; Sp. ^., spinal 
ganglion ; V.R., ventral root of spinal nerve ; Sp. N., 
spinal nerve; i^c, communicating branch {ramus 
comniunicaus) ; S.G., sympathetic ganglion. 



[Chap. VII. 

cranial nerves, except that in these either one root or the other 
is often entirely lacking. 

The relations of the roots, fibres, and so forth, can be best 
understood from a study of the accompanying diagrams (Figs. 
71, 72). 

Degeneration and regeneration of nerves. — Since, as has been stated 
in Chapter 1., the nucleus is essential for the nutrition of the whole cell, it 
follows that if the processes of a neurone are cut off, they will suffer from 
malnutrition and die. If, for instance, a spinal nerve be cut, all the periph- 
eral part will die, since the fibres composing it have been cut off from 
their cell-bodies situated in the cord, or in the spinal ganglia. The divided 
ends of a nerve that has been cut across readily reunite by cicatricial 
tissue, — that is to say, the connective tissue framework unites, — but the 


Fig. 72. — Diaoram showing Relation of Neurones composing the Spinal 
Nerve-koots with Adjacent Nervous Structures. S.E., seusory epithelium 
connected by a sensory neurone with spinal cord ; ^'.3/., striated muscle receiving the 
axons from a motor-cell in the ventral horn of the gray matter in the cord ; Sp. F., 
spinal fibres, medullat«d, sensory, and the motor, pas.sing to the sympathetic gan- 
glion where they connect with the sympathetic neurones; S.F., S.F., non-meduUated 
fibres from the sympathetic neurones passing to the viscera, the axoues going to the 
plain muscle {P.M.), the dendrones to the sensory endings (S.E.). 

cut ends of the fibres themselves do not unite. On the contrary, the periph- 
eral or severed portion of the nerve begins to degenerate, the medullary 
sheath breaks up into a mass of fatty molecules and is gradually absorbed, 
and finally the axone also disappears. In regeneration, the new fibres grow from the axones of the central end of the severed nerve-trunk, and 
penetrating into the peripheral end of the trunk, grow along this as the 
axone of the new nerve, each axone becoming after a time surrounded with 
a medullary sheath. Restoration of function in the nerve may not occur 
for several months, during which time it is presumed the new nerve-fibres are 
slowly finding their way along the course of those which have been destroyed. 


Brain and cranial nerves. — The brain, the most complex and 
largest mass of nervous tissue in the body, is contained in the 
complete bony cavity formed by the bones of the cranium. It 
is covered by three membranes (also named meninges), — the 
dura mater, pia mater, and arachnoid. 

The dura mater, a dense membrane of fibrous connective tissue, 
lines the bones of the skull, foi'ming their internal periosteum, 
and covers the brain. It sends numerous j)rolongations in- 
wards for the support and protection of the different parts of 
the brain ; it also forms sheaths for the nerves passing out of 
the skull. It may be called the protective membrane. 

The pia mater is a delicate membrane of connective tissue, 
containing an exceedingly abundant network of blood and 
lymph vessels. It dips down into all the crevices and depres- 
sions of the brain, carrying the blood-vessels which go to every 
part. It may be called the vascular or nutritive membrane. 

The arachnoid is a delicate membrane which is placed outside 
the pia mater. It passes over the various eminences and de- 
pressions on the surface of the brain, and does not dip down 
into them like the pia mater. Beneath it, between it and the 
pia mater, is space (sub-arachnoid space) in which is a certain 
amount of fluid. The sub-arachnoid space at the base of the 
brain is of considerable size, and contains a large amount of 
this clear limpid fluid, called the cerebro-spinal fluid. This 
fluid probably acts as a sort of protective water-cushion to the 
delicate nervous structure, and prevents the effects of concus- 
sions communicated from without. 

The brain is a semi-soft mass of white and gray matter. 
The white matter consists of very small, medullated nerve- 
fibres, running in various directions, and supported by a deli- 
cate connective tissue framework. The gray matter consists 
of cells and fine gray fibres, also supported by connective 

The brain is divided into four principal parts : the cerebrum, 
the cerebellum, the pons Varolii, and the medulla oblongata. 

The medulla oblongata is continuous with the spinal cord, 
which, on passing into the cranial cavity through the foramen 
magnum, widens into an oblong-shaped mass. It is directed 
backwards and downwards, its anterior surface resting on a 
groove in the occipital bone, and its posterior surface forming 



[Chap. VIL 

the floor of a cavity between the two halves or hemispheres of 
the cerebellum. The cavity, called the fourth ventricle, is 
an expanded continuation of a tiny central canal which runs 
throughout the w^hole length of the spinal cord. 

The cerebellum, or little brain, overhangs the fourth ventricle. 
It is of a flattened oblong shape, and measures from three and a 
half inches to four inclies (89 to 102 mm.) transversely, and 
from two to two and a half inches (51 to 63 mm.) from before 
backwards. It is divided in the middle line into two halves 

Fig. 73. — The Base of the Brain. 1, longitudinal fissure; 2, 2, anterior lobes 
of cerebrum; 3, olfactory bulb; 7, optic commissure; 9, 3d nerve; 11, 4th nerve; 
13, 5th nerve; 14, crura cerebri; 15, (ith nerve; Iti, pons Varolii; 17, 7th nerve ; 19, 
8th nerve; 20, medulla oblongata; 21, 9th nerve; 23, 10th nerve; 25, 11th nerve; 
27, 12th nerve; 28, 29, 30, 31, 32, cerebellum. 

or hemispheres by a central depression, each half being sub- 
divided by fissures into smaller portions or lobes. The surface 
of the cerebellum is traversed by numerous curves or furrows, 
which vary in depth. In the medulla oblongata, the gray 
matter is placed in the interior, and the white on the exterior ; 
in the cerebellum, the gray is on the outside, and the white 

The pons Varolii, or bridge of Varolius, lies in front of the 
medulla oblongata. It consists of alternate layers of transverse 


and longitudinal white fibres, intermixed with gray matter. 
The transverse fibres come mainly from the cerebellum, and 
serve to join its two halves. The longitudinal fibres come from 
the medulla oblongata. This bridge is a bond of union between 
the cerebrum, cerebellum, and medulla oblongata. 

The cerebrum is by far the largest part of the brain. It is 
egg-shaped or ovoidal, and fills the whole of the upper portion 
of the skull. It is almost completely divided by the median 
fissure into two hemispheres, the two halves, however, being 
connected in the centre by a broad transverse band of white 
fibres, called the corpus callosum. Each half is subdivided into 

The longitudinal fibres of the medulla oblongata, passing 
through the pons Varolii, become visible in front of the bridge 
as two broad, diverging bundles. These two bundles form what 
are called the crura cerebri, or pillars of the brain, and are situ- 
ated on the under surface of each hemisphere. Between the 
crura cerebri is a narrow passage (aqueduct of Silvius) lead- 
ing from the fourth ventricle into a smaller cavity called the 
third ventricle. In each side wall of the third ventricle is an 
opening (foramen of Monro) which leads into two large cavi- 
ties, the lateral ventricles, and which occupy the centre of each 
half of the cerebrum. (It will be seen from the above descrip- 
tion that the cavities in the centre of the brain are continuous 
with the central canal in the spinal cord, and also that fibres 
from the cord pass into the centre of the cerebrum.) Forming 
the floors of the ventricles, lodged in the crura cerebri, and 
scattered in their neighbourhood, are irregularly shaped masses 
of gray matter, intricately connected with one another and with 
the gray matter in the medulla oblongata. The surface of the 
cerebral hemispheres is folded, the folds or convolutions being 
deeper and more numerous in some brains than others ; the 
whole of the convoluted surface is composed of gray matter, 
i.e. of cell-bodies and naked processes. 

The whole brain appears to consist of a number of isolated 
masses of gray matter — some large, some small — connected 
together by a multitude of meduUated fibres (white matter) 
arranged in perplexing intimacy. But a general arrangement 
may be recognized. The numerous masses of gray matter in 
the interior of the brain may be looked upon as forming a more 


or less continuous column, and as forming the core of the cen- 
tral nervous system, while around it are built up the great 
mass of the cerebrum and the smaller mass of the cerebellum. 
This central core is connected by various bundles of fibres with 
the spinal cord, besides being, as it were, a continuation of the 
gray matter in tlie centre of the cord. It is also connected at 
its upper end, by numberless fibres, to the gray matter on the 
surface of the cerebrum. 

The average weight of the brain in the male is 49| oz. (1403 
grammes)^; in the female, 44 oz. (1247 grammes). It appears 
that the weight of the brain increases rapidly up to the seventh 
year, more slowly to between sixteen and twenty, and still more 
slowly to between thirty and forty, when it reaches its maxi- 
mum. Beyond this age the brain diminishes slowly in weight, 
about an ounce every ten years. The size of the brain bears a 
general relation to the capacity of the individual. Cuvier's 
brain weighed ratlier more than 64 oz. (1814 grammes), while 
the brain of an idiot seldom weighs more than 23 oz. (652 
grammes). The number and depth of the cerebral convolu- 
tions also bear a close relation to intellectual power ; babies and 
idiots have few and shallow folds, while the brains of men of 
intellect are always markedly convoluted. 

The cranial nerves, — The cranial nerves, twelve in number on 
each side, arise from the base of the brain and medulla oblon- 
gata {vide Fig. 73), and pass out through openings in the base 
of the skull. They are named numerically according to the 
order in which they arise from the brain. Other names are 
also given to them derived from the parts to which they are 
distributed, or from their functions. Taken in their order 
from before backwards, they are as follows : — 

1. Olfactory (sensory). 

2. Optic (sensory). 

3. Oculomotor (motor). 

4. Pathetic or Trochlear (motor). 

5. Trifacial or Trigeminal (mixed). 

6. Abducens (motor). 

7. Facial (motor). 

8. Auditory (sensory). 

^ Avoirdupois weights are used in weighing the organs of the body. One oz. 
avoirdupois = 28.35 grammes. 


9. Glossopharyngeal (mixed). 

10. Pneumo-gastric or Vagus (mixed). 

11. Spinal accessory (motor). 

12. Hypo-glossal (motor). 

The olfactory nerve is the special nerve of the sense of smell. Its origin 
is in the olfactory bulb. Its peripheral dendrones pass through the perfo- 
rated plate of the ethmoid bone and are distributed to the mucous mem- 
brane lining the nasal chambers, while the central axones pass backward to 
the brain. 

The optic nerve is the special nerve of the sense of sight. Its cell-bodies 
are situated in the retinal coat of the eye. Part of its central axones ter- 
minate in the same side of the brain, while the remainder cross to terminate 
in a similar region on the opposite side of the brain. This crossing of part 
of the fibres from both eyes forms the optic commissure. 

The oculomotor nerve supplies all the muscles of the eye except the 
superior oblique and the external rectus. It originates in the gray matter 
of the pons Varolii. 

The pathetic or trochlear nerve supplies only the superior oblique mus- 
cle of the eye. It arises close to the preceding nerve. 

The trifacial is the largest of the cranial nerves. Like the spinal nerves 
it has two roots, — a dorsal or sensory (upon which there is a sensory gan- 
glion), and a ventral or motor. The fibres from the two roots coalesce into 
one trunk, and then subdivide into three large branches : the ophthalmic, 
the superior maxillary, and the inferior maxillary. The ophthalmic branch 
is the smallest, and is a sensory nerve. It supplies the eyeball, the lachry- 
mal gland, the mucous lining of the eye and nose, and the skin and muscles 
of the eyebi'ow, forehead, and nose. The superior maxillary, the second 
division of the fifth, is also a sensory nerve and supplies the skin of the 
temple and cheek, the upper teeth, and the mucous lining of the mouth and 
pharynx. The inferior maxillary is the largest of the three divisions of the 
fifth, and is both a sensory and a motor nerve. It sends branches to the 
temple and the external ear ; to the teeth and lower jaw ; to the muscles of 
mastication ; it also supplies the tongue with a special nerve (the lingual) 
of the sense of taste. The cell-bodies of the motor fibres are situated in 
the pons; while those of the sensory fibres, as in the case of the spinal 
nerves, are situated in a ganglion. This ganglion is called the Gasserian 

The abducens nerve supplies the external rectus muscle of the eye. 

The facial nerve is the motor nerve of all the muscles of expression in 
the face ; it also supplies the neck and ear. Its cells of origin, like those of 
the abducens nerve, are situated in the medulla. 

The auditory nei-ve is the special nerve of the sense of hearing. It 
arises from cells which compose the spiral ganglion in the internal ear, to 
•which its dendrones are exclusively distributed. 

The glosso -pharyngeal nerve is distributed, as its name indicates, to the 
tongue and pharynx, being the nerve of sensation to the mucous membrane 


of the pharynx, of motion to the pharyngeal muscles, and the special nerve 
of taste to part of the tongue. 

The pneumogastric nerve has a more extensive distribution than any of 
the other cranial nerves, passing through the neck and thorax to the upper 
part of the abdomen. It contains both motor and sensory fibres. It sup- 
plies the organs of voice and respiration with motor and sensory filaments; 
and the pharynx, oesophagus, stomach, and heart with motor fibres. 

The spinal-accessory nerve consists of two parts : one, the spinal portion, 
and the other, the accessory portion to the tenth nerve. It is a motor nerve 
supplying certain muscles of the neck. It differs from the other cranial 
nerves in arising from the spinal cord, but it leaves the skull by the same 
aperture as the pneumogastric and glosso-pharyngeal. 

The hypoglossal nerve is the n)otor nerve of the tongue. 

It will be observed that of the twelve pairs of cranial nerves, four and a 
part of a fifth, are distributed to the eye, viz. the optic, motor occuli, pa- 
thetic, abducens, and the ophthalmic branch of the fifth. The ear has one 
special nerve, the auditory, and is sparingly supplied with motor and sensory 
fibres from other nerves. The nose has also one special nerve, the olfac- 
tory, and is more abundantly supplied than the ear, with motor and sensory 
fibres from other nerves. The tongue has two special branch nerves of taste, 
— the lingual, a branch of the fifth, and the glossal, a branch of the ninth; 
it has also its own motor nerve, the hypoglossal. 

The physiology of the nervous system. — The physiology of the 
nervous system, though exceedingly complex in its details, is, 
in its essentials, not difficult to understand. 

The simplest nervous mechanism is the reflex arc, and the 
simplest form of nervous activity is "reflex action." Two 
neurones enter into the formation of a reflex arc, a sensory 
neurone and a motor neurone. On applying an appropriate 
stimulus to the peripheral end of the sensory neurone an im- 
pulse is generated which passes along the sensory neurone to 
the nerve centre, and back again to the periphery by the motor 
neurone ; and, since the motor neurone terminates in a muscle 
(or some similar mechanism), we get a muscular response as 
the indirect result of stimulating the sensory nerve. 

The kind of stimulus which will call forth the nerve impulse 
depends on the peripheral terminatiori of the sensory 7ierve, and 
the kind of response which an appropriate stimulus will call 
forth depends on the mode of terminatio7i of the motor nerve. 
Thus light falling on the retinal coat of the eye (the peripheral 
termination of the sensory nerve) generates an impulse which 
passes to the centre by the optic nerve, and returns again by 
the oculomotor nerve to the periphery, the sphincter of the 

Chap. VII.] 



iris (the termination of the motor nerve), which by its contrac- 
tion narrows tlie pupil. Hence arises the well-lino wn phe- 
nomenon of the contraction of the pupil when light falls upon 
the eye. 

Or, again, food passing into the upper part of the intestine 
stimulates the sensory nerves there. The impulse passes to the 
spinal cord, is reflected from this centre toward the periphery, 
and passing along the motor nerve stimulates to contraction the 
appropriate muscular mechanism which causes a flow of bile 
into the intestine. 



Fig. 74. — Reflex Arc (schematic). — 5.0., sensory organ; S.N., sensory neurone ; 
iV.C, nerve centre; M.N., motor neurone; M.O., motor organ. 

Also, stimulation of taste fibres in the mouth causes a reflex 
secretion of the salivary glands. Innumerable examples of this 
kind might be given. Indeed, since physical life has been well 

Fig. 75. — Reflex Arc, as it is approximately in Man. — 1, Nerve terminal, 
or sensory epithelium ; 2, dendrone of sensory neurone ; 3, cell-body in dorsal root 
ganglion; 4, axone of sensory neurone; 5, dendrone of motor neurone ; 6, cell-body 
in ventral horn; 7, axone of motor neurone; 8, end organ — muscle-cell, gland- 
cell, ett. 


defined as the continual response to external stimuli, reflex ac- 
tion, which is the chief method of response, is the most impor- 
tant vital phenomenon peculiar to animals possessing any nervous 
system whatsoever. 

A careful study of Figs. 74 and 75 will make the typical 
reflex path perfectly intelligible to the student, and should on 
no account be omitted. 

All nervous action is fundamentally similar to this typical 
reflex action. Usually the number of neurones involved is 
greater, often very much greater, than two. The fewer tiie 
neurones, the simpler and more obviously machine-like the 
reaction. The more complex the path, the more uncertain and 
variable the reaction. When the path of the impulse does not 
mvolve the cerebrum, the reactions are unconscious and com- 
paratively simple; but if the cerebral cortex be involved, tlie 
passage of the nerve impulse is accompanied by the phenome- 
non of consciousness, and the reaction may be exceedingly com- 
plex, uncertain, and long delayed. These are the characteristics 
of what we call voluntary reactions. But, although the phrase 
•' reflex action " is usually confined to those actions which are 
involuntary and of which we are unconscious, yet all nervous 
action is essentially the same, differing only in the complexity 
of the path followed by the impulse. 

We will now conclude with a summary of the functions of 
the various parts of the nervous system. 

The nerves serve to connect the distant parts of the body 
with the central nervous system. 

The spinal ganglia contain the cells of origin of all the 
peripheral sensory nerve fibres. 

The sympathetic ganglia serve to distribute motor, and to 
collect sensory, impulses. Also in a few cases an afferent im- 
pulse may pass to a ganglion by the dendrone of one sympa- 
thetic neurone, and leave it to pass back again to the periphery 
by the axone of another, the spinal column not being included 
in the arc. Thus the sympathetic ganglia may occasionally act 
as a centre for reflex action. 

The spinal cord, medulla, and pons act as centres for the more 
simple reHexes. In the medulla there are also special centres 
which govern more complex muscular movements, such as the 
vaso-motor centre which controls the calibre of the blood-vessels, 

Chap. VII.] 



and hence the flow of blood to all parts of the body ; and the 
respiratory centre which coordinates the actions of the muscles 
of respiration. 

Fig. 7fi. — Diagram of Nervous System, a, a, cortex of cerebral hemispheres ; 
6, b, cell-body and dendrones of upper motor neurone, situated in cerebral cortex; 
b', axone of upper motor neurone, branching at its termination near the dendrones 
of lower motor neurone: B, B, cell-body and dendrones of lower motor neurone, situ- 
ated in the ventral horn of gray matter in the spinal cord ; B' , axone of lower motor 
neurone passing to its termination in a voluntary muscle tibre B" ■. C, cell-body and 
dendrones of upper sensory neurone, situated in the medulla oblongata; C"C", axones 
of upper sensory neurones, terminating in cortex; c, cell-body of lower sensory neu- 
rone situated in the dorsal root-ganglion ; c'", dendrone of lower motor neurone, con- 
ducting impulses from the periphery to the central nervous system; c", long axone 
of lower sensory neurone, conducting impulses toward the brain ; c', short axone of 
lower sensory neurone, conducting impulses direct to ventral horn. (For the sake of 
simplicity the connections with the cerebellum are cynitted.) 


The cerebellum is a great coordinating centre for impulses 
passing from the cerebral cortex to the voluntary muscles. 

The cerebral cortex is involved in all conscious perceptions 
or sensations, in memory, and in the voluntary movements. 
Different parts of the cortex have been shown to have different 
functions. Thus there are areas for visual and auditory sensa- 
tions ; areas which control the voluntary movements of various 
parts of the body, — the leg, the arm, the hand, etc., each having 
its separate area.^ There is also a well-defined " speech centre." 

1 All the fibres passing to and from the cortex cross over to the other side of 
the body, so that an injury to one side of the brain causes paralysis of the oppo- 
site side of the body. 



Having studied the four distinctive tissues of the body (the 
epithelial, connective, muscular, and nervous), their structure, 
position in the body, and the various functions they are espe- 
cially adapted to perform, we shall next consider the vascular, 
respiratory, alimentary, and excretory systems, by means of 
which all the tissues are supplied with the materials necessary 
for their life and growth, and relieved of all those waste and 
superfluous matters which are the results of their activity. 

All the tissues of the body are traversed by minute tubes, 
called capillary blood-vessels, to which blood is brought by 
large tubes, called arteries, and from which blood is carried 
away by other large tubes, called veins. These capillaries form 
networks, the meshes of which differ in form and size in the 
different tissues. The meshes of these networks are occupied 
by the elements (cells or their products) of the tissues ; and 
filling up such spaces as exist between the capillary walls and 
the elements of the tissue, is found a colourless fluid, resembling 
in many respects the fluid portion of the blood, and called 
lymph. As the blood flows through the capillaries, certain 
constituents of the blood pass through the capillary wall into 
the lymph, and certain constituents of the lymph pass through 
the capillary wall into the blood within the capillary. There 
is thus an interchange of material between the blood within the 
capillary and the lymph outside. A similar interchange of 
material is at the same time going on between the lymph and 
the tissue itself. Hence, by means of the lymph acting as 
middleman, a double interchange of material takes place 
between the blood within the capillary and the tissue outside 
the capillary. In every tissue, so long as life lasts and the 



blood flows through the blood-vessels, a fluid is passing from 
the blood to the tissue, and from the tissue to the blood. The 
fluid passing from the blood to the tissue carries to the tissue 
the material which the tissue needs for building itself up and 
for doing its work, including the all-important oxygen. The 
fluid passing from the tissue to the blood carries into the blood 
certain of the products of the chemical changes which have 
been taking place in the tissue — products which may be simply 
waste, to be cast out of the body as soon as possible, or which 
may be products capable of being made use of by some other 
tissues. The tissues, by the help of the lymph, live on the blood, 
and the blood may thus be regarded as an internal medium, 
bearing the same relations to the tissue that the external 
medium, the world, does to the whole individaal. Just as the 
whole body lives on the air and food around it, so do the several 
tissues live on the complex fluid by which they are all bathed, 
and which is to them their immediate air and food. 

The blood. — The most striking external feature of the blood 
is its well-known colour, which is bright red approaching to 
scarlet in the arteries, but of a dark-red or purple tint in the 
veins. It is a somewhat sticky liquid, a little heavier than 
water, its specific gravity being about 1.055; it has a saltish 
taste, a slight alkaline reaction, and a temperature of about 
100° F. (37.8° C). 

Seen with the naked eye the blood appears opaque and homo- 
geneous ; but when examined with a microscope it is seen to 
consist of a transparent' almost colourless fluid, with minute 
solid particles immersed in it. The colourless fluid is named 
plasma, the solid particles corpuscles. These corpuscles are of 
two kinds, the red or coloured, and the white or colourless. In 
a cubic millimetre ^ of healthy blood there are on an average 
5,000,000 red corpuscles and 10,000 white. The number of 
white varies much more than that of the red ; the proportion 
of white to the red is usually given at from 1 to 250 up to 
1 to 1000. 

Red corpuscles of the blood. — The red corpuscles have a nearly 

circuUir outline like a piece of coin, and most of them have a 

shallow, dimple-like depression on both sides; their shape is, 

therefore, that of biconcave disks. The average size is ^^q-q of 

1 A millimetre is equal to 0.089, or ^V of an English inch. 



an inch (0.008 mm.) in diameter, and about one-fourth that 
in thickness. When viewed singly by transmitted light the 
coloured corpuscles do 
not appear red, but ^ /nTTT'^ 
merely of a reddish-yel- 
low tinge, or yellowish- 
green in venous blood. 
It is only when the light 
shines upon a number 
of corpuscles that a dis- 
tinct red colour is pro- 
duced. When blood is 
drawn from the vessels, 
the red disks sink in 
the plasma : they have 
a singular tendency to 
run together, and to 

cohere by their broad kk;. TT.-Kku and white Corpuscles of 

surfaces so as to form the Blood. Magnified. ^, moderately magnified, 

the red corpuscles are seen in rouleaux; a, a, 

cylindrical columns like white corpuscles ; B, C, D, red corpuscles, highly 

■niloc! f\y rniilocm-sr nf magnified, Seen in different positions ; J5^, a red cor- 

^ ... puscle swollen into a sphere by imbibition of water; 

coins, and the piles join F, <?, white corpuscles, highly magnified; A", white 

flnpni<!Plvp« f-no-pthpv in corpuscle treated with acetic acid ; if, /, red cor- 

tnemselves tOgemei in puscles wrinkled or crenated. 

an irregular network. 

Generally the corpuscles separate on a slight impulse, and may 

then unite again. 

Each red corpuscle is composed of an external colourless enve- 
lope u'ith coloured fluid contents. — Quain. 

The envelope is a very delicate membrane of a fatty nature, 
and may be ruptured or dissolved under certain conditions. 
The colour of the fluid contents is due to a crystallizable sub- 
stance called haemoglobin. 1 If water be added to a preparation 
of blood under the microscope, the water passes into the cor- 
puscle, and the concave sides of the corpuscle become bulged 
out so that it is rendered globular. By the further action of 
water the hemoglobin is dissolved out of the corpuscle, and 
the colourless envelope remains as a faint circular outline. On 
the other hand, the addition of salt to a preparation of blood by 

1 Haemoglobin is a compound proteid, i.e. its molecules consist of a proteid 
portion, and of a pigment portion, the latter containing one atom of iron. 



absorbing the water causes the corpuscles to shrink, and become 
wrinkled or crenated. Tlie red corpuscles are practically small 
flattened bags, or sacs, the form of which may be clianged by 
altering the density of the plasma. They are very soft, flexible, 
and elastic, so that they are readily squeezed through apertures 
and passages narrower than their own diameters, and when 
pressure is withdrawn, immediately resume their proper shape. 

Function of the red corpuscles. — The red corpuscles, or ery- 
throcytes, by virtue of the hiemoglobin which they contain, are 
emphatically oxygen carriers. Exposed to the air in the lungs, 
the hiemoglobin combines with the oxygen present in the air ; 
this oxygen the haemoglobin carries to the tissues ; these, more 
greedy of oxygen than hsemoglobin itself, rob it of its charge, 
and the haemoglobin, thus deprived of its oxygen, hurries back 
to the lungs for a supply.^ The utility of the haemo- 
globin consists in the ease with which under certain conditions 
(those existing in the lungs) it takes up oxygen, and the 
readiness with which under certain conditions (those existing 
in the capillaries) it gives up this oxygen again. The colour 
of the blood is dependent upon this combination of the 
haemoglobin with oxygen ; when the haemoglobin has its full 
complement of oxygen, the blood has a bright red hue ; when 
the amount is decreased, it changes to a dark purplish hue. 
The scarlet blood is usually found in the arteries, and is 
called arterial ; the dark purple in the veins, and is called 
venous blood. 

White corpuscles of the blood. — The white, colourless corpus- 
cles, or leucocytes, are few in number compared with the red, 
and both on this account, and because of their want of colour, 
they are not at first easily recognized in a microscopic prepara- 
tion of blood. Their form is very various, but when the blood 
is first drawn they are rounded or spheroidal. Measured in 
this condition they are about 2~5Vo ^^ ^'^ ^"^^^ (0.010 mm.) 
in diameter. The white corpuscle may be taken as the type of 
a free animal cell. It is a small piece of protoplasm, contain- 
ing a nucleus, and has no limiting membrane or cell-wall {vide 

These corpuscles, or cells, possess the power of spontaneous 

1 Processes which are characterized by combination with oxygen are known 
as oxidation, while the reverse processes are known as reduction. 


movement, and are capable of changing their form and place. 
While, when in a state of rest, they assume in general the 
spheroidal form, we find that when they become active they 
send out variously shaped processes, some fine and delicate, 
others broad, and of very irregular shape. We often see, after 
a process has been thrown out, that it becomes larger and 
larger, the cell-body becoming correspondingly smaller, until 
finally the whole cell passes over into the process, thus moving 
forward. These amoeboid movements are always very slow, 
and are greatly influenced by the temperature, density, and 
amount of oxygen in the fluid in which the cells lie. By virtue 
of this locomotive power the white blood cells perform certain 
evolutions within the blood-vessels ; they also escape through 
their walls, and sometimes singly, sometimes in vast numbers, 
move through the lymph spaces in the surrounding tissues. 
This is spoken of as the "migration of the white corpuscles." 
In an "inflamed area" large numbers of white corpuscles are 
thus drained away from the blood. These migrating corpuscles, 
or wandering cells, may, by following the devious tracks of the 
lymph, find their way back into the blood ; some of them, how- 
ever, may remain and undergo various changes. Thus in in- 
flamed areas, when suppuration follows inflammation, the white 
corpuscles which have migrated may become "pus corpuscles." 

Again, by virtue of their amoeboid movements, the white 
corpuscles can creep around objects, enveloping them with their 
own substance, and so putting them inside themselves. As an 
illustration of this action of the white corpuscle, we may state 
that, according to some observers in certain diseases in which 
micro-organisms make their appearance in the blood, the white 
corpuscles take up these micro-organisms into their substance, 
and probably exert an influence over them, which modifies the 
course of the disease of which these micro-organisms are the 
essential cause. 

Furthermore, the white corpuscles are not only capable of 
taking up particles in the blood, but are also capable of giving 
up products which they have changed or modified, to the blood, 
and it follows that these metabolic changes must necessarily 
affect the composition of the fluid plasma in which they lie. 

The plasma of the blood. — The plasma is a clear, slightly 
yellowish coloured fluid, consisting for the most part of water, 


holding in solution or suspension proteid substances, fats, 
various extractives, and salts. 

The proteid substances are albumin, para-globulin, and fibrin- 
ogen. The albumin and para-globulin occur in about equal 
quantities; but the fibrinogen, though a most important ele- 
ment in the blood, occurs in very small quantities. The fats are 
scanty, except after a meal, or in certain diseased conditions. 
The extractives, so named because they have to be extracted by 
special methods from the blood, are very numerous. The most 
important are perhaps urea, lactic acid, and sugar. 

Tlie salts in the plasma are the chlorides and sodium salts, 
the phosphates and potassium salts being found chiefly in the 

Of all these substances, albumin probably holds the first place 
in regard to nutrition, providing, as it does, the greater part of 
the material necessary for the daily nourishment and renovation 
of the tissues. In this process it undergoes a variety of trans- 
formations by which it is converted into the structural charac- 
teristics of the tissues which it supplies. 

Para-globulin is closely allied to albumin in its chemical rela- 
tions, and no doubt also in its physiological action. Both sub- 
stances are coagulated by heat, and solidified at a temperature 
of 160° F. (71.1° C). 

The fibrinogen of the plasma is the substance which produces 
the fibrin of coagulated blood. It is very difficult to obtain 
in the fluid condition, owing to the rapidity with which it 
solidifies when blood is withdrawn from the circulation. 

Of the mineral salts, the sodium chloride is the most abun- 
dant, constituting nearly 40 per cent of all the saline ingredi- 
ents. The mineral salts maintain the alkalinity of the blood, 
a property which is essential to nutrition, and even to the 
immediate continuance of life, since it enables the plasma to 
take up the carbon dioxide from the tissues and return it to the 
lungs for elimination. 

The clotting of blood. — Blood when drawn from the blood- 
vessels of a living body is perfectly fluid. In a short time it 
becomes viscid, and this viscidity increases rapidly until the 
whole mass of blood becomes a complete jelly. If the blood in 
this jelly stage be left untouclied in a glass vessel, a few drops 
of an almost colourless fluid soon make their appearance on the 


surface of the jelly. Increasing in number and running together, 
the drops after a while form a superficial layer of pale straw- 
coloured fluid. Later on, similar layers of the same fluid are 
seen at the sides, and finally at the bottom of the jelly, which, 
shrunk to a smaller size and of firmer consistency, now forms a 
clot or crassamentum, floating in a liquid. The upper surface 
of the clot is generally slightly concave. If a portion of the 
clot be examined under the microscope, it is seen to consist of a 
network of fine fibrils in the meshes of which are entangled the 
red and white corpuscles of the blood. The fibrils are composed 
of the fibrin ; and the liquid in which the clot is suspended is 
blood minus corpuscles and fibrin, and is called serum. The 
clotting of the blood is entirely dejDcndent upon the fibrin ; for 
if fresh blood, before it has time to clot, be whipped with a 
bundle of twigs, the fibrin will form on the twigs, and if the 
whipping of the blood be continued until all the fibrin has been 
deposited on the twigs, the blood left in the vessel will be found 
to have lost all power of clotting. 

The coagulation of blood is hastened by high temperature, 
and by contact with any rough surface or non-livi'ig- material. 
On the other hand, a low temperature retards, taid the addition 
of salt in sufficient quantity prevents, coagulation. After death, 
the blood usually remains a long time fluid in the vessels, and 
it never clots so firmly and completely as when shed. It clots 
first in the larger vessels, but not until several hours after death 
in the smaller vessels. 

The coagulability of the blood differs in difl^erent individuals, 
and in rare cases is so slight that the most trivial operation in- 
volving hemorrhage is attended with great danger. 

The quantity of blood contained in the body is a balance 
struck between the tissues which give to, and those which take 
away from, the blood. Thus the tissues of the alimentarj^ canal 
largel}^ add to the blood water and the material derived from 
food, while the tissues of the excretory organs largely take 
away water, urea, and the other substances resulting from the 
waste of the tissues. From the result of a few observations 
on executed criminals, it has been concluded that the total 
quantity of blood in the human body is about -^^ of the body 

General composition of the blood. — Not only do the several tis- 


sues take up from the blood and give up to the blood different 
thing's at different rates and at different times, but all the 
tissues take up oxygen and give up carbon dioxide in varying 
quantities. From this it follows, on the one hand, that the 
composition and character of the blood must be forever varying 
in different parts of the body ; and, on the other hand, that the 
united action of all the tissues must tend to establish and main- 
tain an average uniform composition of the whole mass of blood. 
To sum up briefly, the blood is composed of — 


Proteid substances. 



r Red 
Corpuscles \ and 

[ White. 

The plasma is chiefly the carrier of nutriment to the tissues, 
and of waste matter from the tissues. The red corpuscles are 
pre-eminently the carriers of oxygen ; the white corpuscles may 
be regarded as scavengers, us important protective elements in 
many diseases, and jjossibly as contributors to the construction 
of new tissue where such has been injured or destroyed. 

Note. — When we remember that the tissues live on the blood, we recognize 
the gravity of those diseased conditions in which important elements are being 
constantly drained away from the blood, as, for example, the albumin in dis- 
eases of the kidneys, the red corpuscles in hemorrhage, the water of the blood 
in cholera, etc. Withdrawal of oxygen, as we all know, causes instant death, 
and a constant supply of fresh air is a vital necessity of life. Nor is it of less 
importance that the blood be kept free from those waste matters, — pre-eminently 
carbon dioxide and urea, — which, in accumulating, poison the system, and. if 
not excreted in sufficient amount, will as surely cause death as the withdrawal 
from the blood of any of its most vital constituents. 



The blood, as we have said, is the internal medium on which 
the tissues live. It is carried through the body by branched 
tubes named blood-vessels. It is driven along these tubes by 
the action of the heart, which is a hollow muscular organ placed 
in the centre of the vascular system. One set of vessels — the 
arteries — conducts the blood out from the heart and distributes 
it to the different parts of the body, whilst other vessels — the 
veins — bring it back to the heart again. The blood from the 
arteries gets into the veins by passing through a network of 
fine tubes which connect the two, and which are named, on 
account of their small size, the capillary (^i.e. hair-like) vessels. 

All the tissues except the epithelial and cartilaginous tis- 
sues are traversed by these networks of capillary vessels. 
It is through the thin walls of the capillaries that the inter- 
change of material which is continually going on between the 
blood and the tissues takes place. It is in the capillaries, then, 
that the chief work of the blood is done ; and the object of the 
vascular mechanism is to cause the blood to flow throusfh these 
vessels in the manner best adapted for accomplishing this work. 

The use of the arteries is to carry and regulate the supply of 
blood from the heart to the capillaries; the use of the veins, to 
carry the blood from the capillaries back to the heart ; the use 
of the heart, to drive the blood in a suitable manner through 
the arteries into the capillaries, and from the capillaries back 
along the veins to itself again. We shall see that the structure 
of these several parts is adapted to these several uses. 

The heart. — The heart is a hollow muscular organ, divided 
by a longitudinal partition into a right and a left heart, each of 
which is subdivided by a transverse constriction into two com- 
partments, an upper and a lower, which communicate with each 




[Chap. IX. 

other. Its general form is tliat of a blunt cone. It is situated 
in the thorax, between the lungs, and, together with the adja- 
cent parts of the great blood-vessels which carry blood to and 
from it, is enclosed in a membranous covering, the pericardium. 

The heart lies nearer 
to the front than to 
the back of the chest, 
and is placed behind 
the sternum and the 
costal cartilages, the 
broader end or base 
being directed up- 
wards, backwards, and 
to the right, while the 
pointed end or apex 
points downwards, for- 
wards, and to tlie left. 
The impulse of the 
heart against the wall 

Fig 78. -The Heart AND LUKU«. x, nght ven- ^^ ^^^^ ^j^^^^ • ^^^^ -^^ 
tricle; o, right auricle; b, 7, pulmonary artery; 9, 

aorta; 10, superior vena cava; 11, innominate ar- the spaCC between the 

tery; 12, right subclavian vein ; 14, innominate vein; nr,^ , -i -,0.1 ,m 

15,'left common carotid; 17, trachea; 20, pulmonary "^^'^ '^^^^^ SlXtU riDS, a 

veins; 22 to 25, lungs, partially turned back to show little below and tO the 

veins on left side. . . . c n 1 f, 

inner side oi tlie left 
nipple. It has, therefore, a very oblique position in the chest. 
It is suspended and kept in position by the great vessels at the 
base, and is also supported by the diaphragm. According to 
Laennec, the heart in its normal condition is about equal in 
size to the fist of the individual to whom it belongs. 

The main substance of the lieart is composed of muscular 
tissue. Between the muscle fibres is a certain amount of in- 
terstitial tissue with numerous blood-vessels and lymphatics, 
and, in some parts, nerves and ganglia. There is also a consid- 
erable amount of fat, chiefly collected at the base of the heart, 
and beneath the pericardium. The muscular tissue of the heart 
differs from all other involuntary muscular tissue in possessing 
transverse striae. The fibres continually branch and unite with 
one another so as to form a kind of network or sponge-like sub- 
stance. The arrangement of the fibres differs in the auricles 
and the ventricles, and is very intricate; the fibres run trans- 

Chap. IX.] 



versely, longitudinally, obliquely, and in the apex of the ven- 
tricles take a spiral turn or twist. The muscular walls of the 
auricles are much thinner than those of the ventricles, and the 
wall of the left ventricle is thicker than that of the right. 
This difference in bulk is 
to be accounted for, as 
we shall see later on, by 
the greater amount of 
work the ventricles, as 
compared with the auri- 
cles, have to do. The 
muscular walls of the 
heart are abundantly 
supplied with blood 
and lymph. The nerves 
which supply the heart 
are partly derived from 
the cerebro-spinal system, 
and partly from the sym- 
pathetic system. Con- 
nected with the nerve 
fibres supplying the heart fiq. 79. _ anterior View of heart, Dis- 

are groups of nerve cells, sected, after Long Boiling, to sh..w the 

° 7 Superficial Muscular Fibres. (Allen Thom- 

Or ganglia. son.) The aorta {¥) and pulmonary artery (a') 

Thp heart is covered ^^^^'^ been cut short close to the semilunar valves. 

' a, right ventricle; b, left ventricle; c, c, groove 

as mentioned above, by a between ventricles; d, c?', right auricle; e, e', left 

1 • • auricle: /", superior vena cava; r/', r/", right and 

membranous covering m ^^^^ pulmonary veins. The fibres are seen run- 

the form of a sac. This ning in a circular, oblique, transverse, and longi- 

, . tudinal direction. 

membranous sac, or peri- 
cardium, is one of the serous membranes of the body.^ It is a 
sort of double bag ; one half of the bag, called the visceral por- 
tion (yiscus, organ), is closely adherent to the heart substance, 
and also covers the great blood-vessels for about an inch and a 
half (38 mm.) from the base of the heart ; the other half, the 
parietal portion, is continuous with, and reflected over, the vis- 
ceral portion, so that it loosely envelops both it and the heart. 
The pericardium forms a completely closed sac ; its internal 
surfaces are very smooth and polished, they are lined by endo- 
thelium (see note on p. Ill) and secrete a small quantity of 
1 See note on serous membranes at end of chapter. 



[Chap. IX. 

Fig. 80. — Diagram of Heart and Peri- 
cardium. In A, heart and pericardium lying 
separately. In B, pericardium lying around 
heart. 7/, heart; P, pericardium; P.O. peri- 
cardial cavity ; P.P. parietal portion of pericar- 
dium ; V.P. visceral portion. 

serous fluid. As their 
opposing surfaces, owing 
to the constant contrac- 
tions of the heart, are 
continually sliding one 
upon the other, they are 
admirably constructed to 
protect the heart from any 
loss of power by friction. 
The interior of the 
heart is lined by a deli- 
cate, smooth membrane, 
called the endocardium. 
This pavement membrane lines all the cavities of the heart, 

and is continued into 
the blood-vessels, form- 
ing their innermost coat. 
The cavities of the 
heart. — The heart is 
divided from the base 
to the apex, by a fixed 
partition, into a right 
and left half. The two 
sides of the heart have 
no communication with 
ch other: the right 
side always contains 
venous, and the left 
ide arterial, blood. 
Each half is sub- 
divided into two 
cavities, the up- 
per, called auri- 
cle ; the lower, 
ventricle. These 
cavities com- 
municate with 
Fig. 81. — Right Side of Heart. A, cavity of right ven- .-, i 

tricle ; 5, sup. vena cava; C, inf. vena cava; «, wall of right ^^^® anotner Dy 
ventricle; 6, c, columnie carneae ; r/, pulmonary vein ; e,/, tri- means of COn- 
cuspid valve; m, semilunar valve; o, wall of left ventricle ; . • - i 
p, q, V, ascending aorta, arch and descending aorta. StriCtecl Open- 

Chap. IX.] 



ings, the auriculo-ventricular orifices, which are strengthened 
by fibrous rings, and protected and guarded by valves. The 
valve guarding the right auriculo-ventricular opening is com- 
posed of three triangular flaps, and is hence named tricuspid. 
The flaps are mainly formed of fibrous tissue covered by endo- 
cardium. At their bases they are continuous with one another, 
and form a ring-shaped membrane around the margin of the 
auricular opening: their pointed ends are directed downwards, 
and are attached by cords, the cliordoe tendi- 
nece, to little muscular pillars, the cohmi- 
noB carneoe^ provided in the interior 
of the ventricles for this purpose. 
The valve guarding the left 
auricular oj)ening consists 
of only two flaps, and is 
named the bicuspid, or 
mitral valve. It is 
attached in the 
same manner as 
the tricuspid 
valve, which it 
closely resem- 
bles in struc 
ture, except 
that it is much 
stronger and 
thicker in all 
its parts. 

Fio. SJ — 

IjFFI biDh OF 

[k\rt l.cav- 
)f left aiiiiele; 
ppTiinij of riglit 
pulmonary veins , .''), left 
pnlnionary veins , 6, auri- 
i lll()-^ ('Utricular openiiiE: , 8, w all 
of left ^entric]e, '» caMty of left ven- 
tricle; a, mitral valve (its flaps are attached by the chord® tendineae to the mus- 
cular pillars (6, h) ; d, arch of aorta) ; e, pulmonary artery. 

These valves oppose no obstacle to the passage of the blood 
from the auricles into the ventricles; but any flow forced back- 
wards gets behind the flaps of the valve (between the flap and 
the wall of the ventricle) and drives the flaps backwards and 
upwards, until, meeting at their edges, they unite and form 
a complete transverse partition between the ventricle and auri- 
cle. Being retained by the chordse tendinese, the expanded 
flaps of the valve resist any pressure of the blood which might 
otherwise force them back to open into the auricle; the mus- 
cular pillars, also, to which the chordse tendinese are attached. 



[Chap. IX. 

contract and shorten at the same time, and thus keep them 

Besides the openings between the auricles and ventricles, each 
auricle has two or more veins opening into it, and each ventricle 
has a large artery opening out of it. The openings of the veins do 
not require valves, but both the arterial openings are provided 
with a set of valves. These valves, called seanilunar valves, con- 
sist of three semicircular flaps, each flap being attached at its 
base to the inside of the artery where it joins the ventricle, 
while its free edge projects into the interior of the vessel. The 



Fig. 83. — Diagram to illustrate the Action of the Heart, aur, auricle; 
vent, ventricle; v, veins; a, aorta; m, mitral valve; s, semilunar valves. In A, 
auricle is seen contracting, ventricle dilated, mitral valve open, semilunar valves 
closed. In B, auricle is seen dilated, ventricle contracting, mitral valve closed, 
semilunar valves open. 

flaps of these valves form a complete barrier, when closed, to 
the passage of the blood from the arteries into the heart, but 
offer no resistance to the flow from the heart into the arteries. 
The beat of the heart. — So long as life lasts, the muscular 
tissue of the heart contracts and relaxes unceasingly. We may 
call the heart a muscular pump, the force of whose strokes is 
supplied by the contraction of muscular fibres, the strokes being 
repeated so many times a minute. It is constructed and fur- 
nished with valves in such a way that, at each stroke, it drives 
a certain quantity of blood with a certain force and a certain 
rapidity from the ventricles into the arteries, receiving, during 
the stroke, and the interval between that stroke and the next, 
the same quantity of blood from the veins into the auricles. 

Chap. IX.] 



The contractions of the heart are rhythmical; that is to say, 
they occur in a certain order. First, there is a simultaneous 
contraction of the walls of both auricles; immediately following 
this, a simultaneous contraction of both ventricles; then comes 
a pause, or period of rest, after which the auricles and ven- 
tricles contract again in the same order as before, and their 
contractions are followed by the same pause as before. The 
state of contraction of the 
heart is called the systole ; 
the state of relaxation and 
dilatation, its diastole. 

If the chest of an ani- 
mal be opened and arti- 
ficial respiration kept up, 
the heart may be watched 
beating, and a complete 
beat of the whole heart 
may be observed to take 
place as follows : — 

The great veins are 
seen, while full of blood, 
to contract in the neigh- 
bourhood of the heart, 
the wave of contraction 
running on towards the 
auricles, increasing in in- 
tensity as it goes. Arrived at the auricles, which are now full 
of blood, the wave of contraction passes on to them, and they 
contract suddenly and quickl3^ During this contraction, the 
walls of the auricles press towards the auriculo-ventricular ori- 
fices, and the blood passes over the tricuspid and mitral valves 
into the ventricles. The ventricles fill rapidly, and as soon as 
the auricular contraction is over, they in turn are seen to con- 
tract, their walls becoming very tense and hard; the apex is tilted 
upwards, and the heart twists somewhat on its own axis. Dur- 
ing the ventricular contraction the blood in the ventricles is 
forced through the semilunar valves into the arteries, which are 
seen to elongate and expand as the blood is pumped into them. 

The work of the auricles and ventricles is very unequal. All 
the auricles have to do is to pump the blood into the ventricles, 

Fig. 84. — Section of Heart at Level of 
Valves. P, pulmonary artery, with Haps of 
semilunar valve open; A, aorta, with flaps of 
semilunar valve open ; M, closed mitral valve ; 
T, closed tricuspid valve. 


which at the time are nearly empty cavities with relaxed and 
flaccid walls. The ventricles, on the contrary, have to pump the 
blood into tubes which are already full; and if there were no 
auriculo-ventricular valves, the blood would meet with less resist- 
ance in pushing its way backward into the auricles than in push- 
ing open the semilunar valves and forcing its way into the arteries. 
Hence the necessity, first, of the tricuspid and mitral valves; 
and, secondly, of the superior thickness and strength of the 
walls of the ventricles, as compared with those of the auricles ; 
and since the left side of the heart has a larger sj'stem of blood- 
vessels to supply, and more resistance to overcome, than the 
right side, it follows that the left ventricle needs a thicker 
muscular wall than the right. 

The beat of the heart is caused by the rhythmical contractions 
of its muscular fibres. Whether these contractions are auto- 
matic or dependent upon the ganglia lodged in the cardiac 
muscular tissue, is uncertain. That the contractions of the 
heart do not depend upon the general nervous system is certain, 
for the heart will continue to beat for some little time after its 
removal from the body. It probably depends upon complex 
metabolic changes, not yet clearly understood. 

The character of the beat, however, is governed and regulated 
by two sets of nerves. The first set come from the cerebro-spinal 
centre, and are supplied by the pneumogastric nerves. They are 
the inhibitory fibres; that is to say, they slow and, with a strong 
stimulation, will stop for a short time the action of the heart. 
They weaken the systole, and prolong the diastole. The other 
set come from the sympathetic nerves, and are accelerating fibres 
which, upon stimulation, increase not only the rapidity, but the 
force of the beat. The diastole is shortened, and the systole 

The sounds of the heart. — If the ear be applied over the heart, 
certain sounds are heard, which recur with great regularity. 
The first sound is a comparatively long, booming sound; the 
second, a short, sharp, sudden one. Between the first and 
second sounds, the interval of time is very short, too short to 
be measurable; but, between the second and the succeeding first 
sounds there is a distinct pause. The first sound is generally 
supposed to be caused by the contraction of the ventricular 
walls; the second sound is undoubtedly caused by the sudden 
closure of the semilunar valves. 

Chap. IX.] 



These sounds in certain diseases of the heart become changed 
and obscure, and are replaced by various distinctive and charac- 
teristic murmurs. 

The arteries. — An artery is usually described as being com- 
posed of three coats, — an inner or elastic, a middle or muscular, 
and an external or areolar. 

The inner coat of an artery consists of two layers : the inner 
layer is composed of endothelium,^ 
and forms a smooth lining for the 
tube; the outer layer is a fine net- 
work of elastic connective tissue 

The middle or muscular coat con- 
sists mainl}'" of circularly disposed 
plain muscular fibres. It has also 
in most large arteries layers of elas- 
tic fibres, which form close felted 
networks, the fibres running for the 
most part in an oblique and longi- 
tudinal direction. 

The outer coat is formed of areo- 
lar tissue, mixed with which are a 
good many elastic fibres. The 
strength of an artery depends largely 
upon this coat; it is far less easily cut or torn than the other 
coats, and it serves to resist undue expansion of the vessel. 
The arteries are also protected by sheaths of connective tissue, 
which surround and blend with the outer coat. 

By virtue of their structure, the arteries are both contractile 
and elastic. The proj)ortion of the muscular and elastic ele- 
ments differs in different arteries; but, as a general rule, the 
larger arteries are the more elastic, and the smaller the more 
muscular. The elasticity and contractility of the arteries may 
be demonstrated by the following example : — 

If we tie a piece of a large artery at one end and inject fluid 

1 Endothelium is the name now generally given to the variety of epithelium 
lining {i.e. lying xmthin) certain parts of the body ; it is composed of flattened, 
transparent cells joined edge to edge so as to form smooth membranes. It is 
found on the free surfaces of the serous membranes ; as the lining membrane of 
the heart, blood-vessels, and lymphatics ; on the surface of the brain and spinal 
cord, and iu the anterior chamber of the eye. 

Fig. 85. — Structure of an Ar- 
tery. (Ledig.) A, internal coat, 
with h, its inner layer of pavement 
epithelium (endothelium); c, middle 
coat, with transverse fibres; d, outer 
coat, with longitudinal fibres. 



[Chap. IX. 

into the other end, the artery swells out to a very great extent, 
but will return at once to its former size when the fluid is let 
out. This great elasticity of the arteries adapts them for 
receiving the additional amount of blood thrown into them 
at each contraction of the heart. Again, if we stimulate the 
muscular coat of any of the smaller arteries, the artery will 
shrink in size, the circularly disposed fibres contracting and 
narrowing the calibre of the vessel. This contractility is under 
the control of the nervous system, and as the organs of the 
body that are at rest do not require so much blood as those that 
are working actively, the nervous system, the master-regulator 
of the body's work, is able to diminish or increase the supply of 
blood to the capillaries in different parts by acting upon this 
contractile muscular tissue in the arterial walls. The arteries 
do not collapse when empty; and when an artery is severed, the 
orifice remains open. The muscular coat, however, contracts 
jl 15 somewhat in the neighbourhood of the 

opening, and the elastic fibres cause the 
artery to retract a little within its sheath. ^ 
The walls of the arteries are supplied with 
both blood-vessels and nerves. The blood- 
vessels are known as the vaso-vasorum ves- 
sels and the nerves as the vaso-motor nerves. 
The veins. — The veins have three coats, 
and on the whole resemble the arteries in 
structure. They differ from them, how- 
ever, in having much thinner walls, and 
in their walls containing relatively much 
more white fibrous tissue and much less 
yellow elastic tissue. They are, therefore, not so elastic or con- 
tractile as the arteries, and their walls collapse when empty. 
Many of the veins, especially those of the limbs, are provided 
with valves, which are mechanical contrivances adapted to pre- 
vent the reflux of the blood. The valves are semilunar folds of 
the internal coat of the veins; the convex border is attached to 
the side of the vein, and the free edge points towards the heart. 
Should the blood in its onward course towards the heart be, for 
any reason, driven backwards, the refluent blood, getting be- 
tween the wall of the vein and the flaps of the valve, will press 
1 This property of the severed artery is an important factor in the arrest of 

Fig. 86. — ^, part of a 
vein, laid open, with two 
pairs of valves; B, longi- 
tudinal section of vein, 
showing valves closed. 


them inwards until their edges meet in the middle of the chan- 
nel and close it up. The valves have usually two flaps, some- 
times one, and rarely three. The veins, like the arteries, are 
supplied with both blood-vessels and nerves, the supply, how- 
ever, being far less abundant. 

The capillaries. — The walls of the capillaries are formed 
entirely of a layer of simple endothelium composed of flat- 
tened cells joined edge to edge by cement substance, and 
continuous with the layer which lines the arteries and veins. 
The capillaries communicate freely with one another and form 
interlacing networks of variable form and size in the different 
tissues. Their diameter is so small that often the blood-cor- 
puscles must pass through them in single file, and in many parts 
they lie so closely together that a pin's point cannot be inserted 
between them. They are most abundant, and form the finest 
networks in those organs where the blood is needed for other 
purposes than local nutrition, such as, for example, for secretion 
or absorption. In the glandular organs they supply the sub- 
stances requisite for secretion; in the alimentary canal they 
take up the elements of digested food; in the lungs they absorb 
oxygen and give up carbonic acid; in the kidneys they discharge 
the waste products collected from other parts; all the time, every- 
where through their walls, that interchange is going on which is 
essential to the renovation, growth, and life of the whole body. 

It must be remembered that although the arteries, veins, and 
capillaries have each the distinctive structure above described, 
it is at the same time difficult to draw the line between the 
smaller artery and larger capillary, and between the larger 
capillary and smallest vein. The veins on leaving the capillary 
networks only gradually assume their several coats, while the 
arteries dispense with their coats in the same imperceptible way 
as they approach the capillaries. 

Serous membranes. — Serous membranes are thin and transparent, tol- 
erably strong, extensile, and elastic. They are lined on the inner snrface by 
a simple epithelial layer of flattened cells (endothelium). The surfaces are 
moistened by a fluid resembling serum, and from which t^e membranes 
obtain their name of serous membranes. Here and there between the cells 
openings are seen, which are of two kinds. The smaller and more numerous 
are false openings, and are termed pseudo-stomata; the larger or true aper- 
tures are termed stomata, and open into subjacent lymphatics. The sub- 
stance of serous membranes underneath the endothelium is composed of a 



[Chap. IX. 

network of connective tissue containing a variable amount of white and 
elastic fibres. Where the membrane is thick, this ground substance contains 
blood-vessels and lymphatics, the lymphatics being exceedingly abundant. 

Serous membranes form closed sacs, one part of which is attached to the 
walls of the cavity which it lines, — the parietal portion, — whilst the other 
is reflected over the surface of the organ or organs contained in the cavity, 
and is named the visceral portion of the membrane. In this way the viscera 
are not contained within the sac, but are really placed outside of it, and 
some of the organs may receive a complete, while others receive only a par- 
tial or scanty, investment. 

In passing from one part to another the serous membrane in the abdomen 
frequently forms folds, some of which are designated by special names, such 
as the mesentery, meso-colon, and omentum. 

Fig. 87.- 

■Portion of Endothelium of Peritoneum. (Klein.) a, larger cells; 
6, smaller ones, with here and there a pseudo-stoma between. 

The chief serous membranes are the peritoneum, the largest of all, lining 
the cavity of the abdomen; the two pleurEB, lining the chest and covering 
the lungs ; the pericardium, covering the heart. 

The peritoneum in the female is an exception to the rule that serous 
membranes are perfectly closed sacs, as it has two openings by which the 
Fallopian tubes communicate with its cavity. 

The inner surface of a serous membrane is free, smooth, and polished; 
the inner surface of one part is applied to the corresponding inner surface 
of some other part, a very small quantity of fluid only being interposed 
between the surfaces. The organs situated in a cavity lined by a serous 
membrane, being themselves also covered by it, can thus glide easily against 
its walls or upon each other, their motions being rendered smoother by the 
lubricating fluid. 



The arteries. — The arteries, which carry and regulate the 
supply of blood from the heart to the capillaries, are distributed 
throughout the body in a systematic manner, and before taking 
up the circulation we must try to gain a general idea of this 
system of distribution, in order that we may be able to locate 
the position of these important vessels. The arteries usually 
occupy protected situations, that they may be exposed as little 
as possible to accidental injury. As they proceed in their 
course they divide into branches, the division taking place in 
different ways. An artery may at once resolve itself into two 
or more branches, no one of which greatly exceeds the rest in 
size ; or it may give off several branches in succession, and still 
maintain its character as a trunk. An artery, after a branch 
has gone off from it, is smaller than before, but usually con- 
tinues uniform in diameter until the next secession. A branch 
of an artery is less in diameter than the trunk from which it 
springs, but the collective capacity of all the branches into 
which an artery divides is greater than the parent vessel. Since 
the area of the arterial system increases as its vessels divide, it 
is evident that the collective capacity of the smaller vessels 
and capillaries must be greater than the collective capacity of 
the trunks from which they arise. As the same rule applies to 
the veins, it follows that the arterial and venous systems may 
be represented, as regards capacity, by two blunt cones whose 
apices are at the heart, and whose bases are united in the cap- 
illary system. The effect of this arrangement of the circulatory 
vessels is to make the blood flow more slowly as it passes 
through the more widely distributed vessels, and to accelerate 
its speed in the larger and less numerous trunks, just as the 
water of a river flows more rapidly through its narrow chan- 
nels, and lingers in those that are broad. 



The arteries unite at frequent intervals when they are said 
to anastomose or inosculate. Such inosculations admit of free 
communication between the currents of the blood, tend to pro- 
mote equality of distribution and of pressure, and to obviate 
the effects of local interruption. . 

Arteries commonly pursue a tolerably straight course, but in 
some parts of the body they are tortuous. The facial artery 
in its course over the face, and the arteries of the lips, are 
extremely tortuous, so that they may accommodate themselves 
to the movements of the parts. The uterine arteries are also 
tortuous, to accommodate themselves to the increase in size of 
the uterus during pregnancy. 

In describing the distribution of the arteries we shall first 
consider the artery arising from the left ventricle of the heart, 
the aorta, and its branches. 

The aorta. — The aorta is the main trunk of the arterial sys- 
tem. Springing from the left ventricle of the heart, it arches 
over the root of the left lung, descends along the vertebral col- 
umn, and after passing through the diaphragm into the abdomi- 
nal cavity, ends opposite the fourth lumbar vertebra by dividing 
into the risfht and left common iliac arteries. In this course 
the aorta forms a continuous single trunk, which gradually 
diminishes in size from its commencement to its termination 
(from 28 to 17 mm.), and gives off larger or smaller branches 
at various points. It may be divided into the ascending aorta, 
the short part which is contained within the pericardium ; the 
arch, the part extending from the ascending aorta, and forming 
a well-marked curve in front of the trachea, and around the root 
of the left lung to the border of the fourth dorsal vertebra ; the 
descending thoracic aorta, the comparatively straight part extend- 
ing to tlie (liai)hragm; the abdominal aorta, below the diaphragm. 
Tlie ascending aorta gives off two small branches, the right and 
left coronary arteries, which supply the substance of the heart 
with bh)()(l. The arch gives off three large trunks, the innomi- 
nate, the left common carotid, and the left subclavian arter3\ 

The innominate artery arises from the right upper surface of 
the arch, ascends obliquely towards the right, until, arriving on 
a level with the upper margin of the clavicle, it divides into 
the right common carotid and right subclavian arteries. Its usual 
lensrth is from one to two inches. 

Chap. X.] 



The left common carotid arises from the middle of the upper 
surface of the arch of the aorta, and the left subclavian arises 
from the left upper surface of the arch. 

^■^r IS 



Figs. 88, 89. — The Aorta. A, from before ; B, from behind, with the origin of its 
principal branches. (R. Quain.) 1, 2, ascending aorta; 2, 3, arch of aorta; 4, innomi- 
nate artery ; 5, left carotid ; (i, left subclavian ; 7,7,7, intercostal and lumbar arteries ; 
8, 8, renal arteries; 0, 9, common iliac arteries ; 10, middle sacral arteries; 11, one of 
the phrenic arteries; +, coeliac axis; 12, gastric; 1.3, hepatic; 14, splenic artery; 15, 
superior mesenteric ; IG, inferior mesenteric : 17, 17, spermatic or ovarian arter'ps. 



[Chap. X. 

The common carotid arteries. — As the left common carotid 
arises from tlie middle of the upper surface of the arch of the 
aorta, while the right common carotid arises at the division of 
the innominate, the left carotid is an inch or two longer than 
the right. They ascend obliquely on either side of the neck 

Fig. 90. — The Carotid, Subclavian, and Axillary Arteries. 1, commcn 
carotid artery ; 2, internal carotid ; 3 and 18, external carotid ; 8, facial artery ; 22, 
subclavian artery ; 28, axillary artery ; 33, commencement of brachial artery. 

until, on a level with the upper border of the thyroid cartilage, 
"Adam's apple," they each divide into tw^o great branches, of 
which one, the external carotid, is distributed to the superficial 
parts of the head and face, and the other, the internal carotid, to 
the brain and eye. At the root of the neck the common carotids 

Chap. X.] 



are separated from each other by only a narrow interval, corre- 
sponding with the width of the trachea; but as they ascend 
they are separated by a much 
larger interval, corresponding with 
the breadth of the larynx and 

The external carotid has eight 
branches, which are distributed 
to the throat, tongue, face, and 
walls of the cranium. 

The chief branches of the in- 
ternal carotid are the ophthalmic 
and cerebral arteries. A remark- 
able anastomosis exists between 
the cerebral arteries at the base of 
the brain. The arteries are joined 
in such a manner as to form a 
complete circle, and this anasto- 
mosis, known as the " circle of 
Willis," both equalizes the circula- 
tion of the blood in the brain, and 
also provides, in case of destruction 
of one of the arteries, for the blood 
reaching the brain through the 
other vessels. 

The subclavian arteries. — The 
right subclavian arises at the 
division of the innominate, and 
the left subclavian from the arcli 
of the aorta. The sul^clavian 
arteries are the first portions of a 
long trunk which forms the main 
artery of the upper limb, and which 
is artificially divided for purposes 
of description into three parts ; 
viz. the subclavian, axillary, and 
brachial arteries. The subclavian 
artery passes a short way up the ^'"^^^y- 

thorax into the neck, and then turns downwards to rest on the 
first rib. At the outer border of the first rib it ceases to be called 

Fig. 91. — Deep Anterior View 
OF THE Arteries of the Arm, 
Forearm, and Hand. A, biceps 
muscle; 1, brachial artery; 4, radial 
artery ; 6, deep palmar arch ; 8, ulnar 


subclavian, and is continued as the axillary. It gives off large 
branches to the back, chest, and neck. 

The axillary artery passes through the axilla, lying to the 
inner side of the shoulder joint and upper part of the arm. It 
gives off branches to chest, shoulder, and arm. 

The brachial artery extends from the axillary space to just 
below the bend of the elbow, where it divides into the ulnar and 
radial arteries. It may be readily located, lying in the depres- 
sion along the inner border of the biceps muscle. Pressure 
made at this point on the artery, from before backwards against 
the humerus, will control the blood supply to the arm. 

The ulnar artery, the larger of the two vessels into which the 
brachial divides, extends along the side of the forearm into 
the palm of the hand, where it terminates in the superficial 
palmar arch. 

The radial artery appears, by its direction, to be a continua- 
tion of the brachial, although it does not equal the ulnar in size. 
It extends along the front of the forearm as far as the lower 
end of the radius, below which it turns round the outer border 
of the wrist, descends between the bones of the thumb and fore- 
finger, and passes forward into the palm of the hand. It ter- 
minates in the deep palmar arch. The superficial and deep 
palmar arches supply the hand with blood. 

The thoracic aorta extends from the lower border of the fourth 
dorsal vertebra, on the left side, to the opening in the diaphragm 
below the last dorsal vertebra, and has a length of from seven 
to eight inches. The branches, derived from the thoracic aorta, 
are numerous, but small. They are distributed to the walls of 
the thorax, and to the viscera contained within it. 

The abdominal aorta commences about the lower border of the 
last dorsal vertebra, and terminates below by dividing into the 
two common iliac arteries. The bifurcation usually takes place 
about half-way down the body of the fourth lumbar vertebra, 
which corresponds to a spot on the front of the abdomen, 
slightly below and to the left of the umbilicus. Its length is 
about five inches. 

The abdominal aorta gives off numerous branches, which may 
be divided into two sets ; viz. those which supply the viscera, 
and those which are distributed to the walls of the abdomen. 
The former set consists of the cceliac axis, the superior mesenteric. 

Plate V — The Abdominal Aorta and its Principal Branches. (Tiede- 
mann) o, ensiform appendix; b, inferior vena cava and c, (Esophagus, passing 
through diaphragm ; /', f, right and left kidneys, with the supra-renal bodies ; g, g 
ureters ; h, urinary bladder ; k, rectum, divided near its upper end. 1, 1, abdominal 
aorta- 2 2', and 3, 3', right and left inferior phrenic arteries; 4, coeliac axis; 5, 
superior mesenteric artery; 6, 6, renal arteries; 7, 7, spermatic or ovarian arteries; 
8, inferior mesenteric artery ; 10, 10, common iliac arteries ; 11, placed between 
external and internal iliac arteries. 




[Chap. X. 

the inferior mesenteric, the supra-renal, the renal, and the sper- 
matic or ovarian arteries, while in the latter are included the 

phrenic, the lumbar, and the 
middle sacral arteries. 

The coeliac artery, or axis, 
is a short, wide vessel, usually 
not more than half an inch in 
length, which arises from the 
front of the aorta, close to the 
opening in the diaphragm. It 
divides into three branches; 
viz. the gastric, which supplies 
the stomach ; the hepatic, 
which supplies the liver; and 
the splenic, which supplies the 
spleen, and in part the stom- 
ach and pancreas. 

The superior mesenteric ar- 
tery arises from the fore part 
of the aorta, a little below 
the coeliac axis. It supplies 
the whole of the small intes- 
tine beyond the first portion 
(the duodenum) close to the 
stomach, and half of the large 

The inferior mesenteric ar- 
tery arises from the front of 
the aorta, about an inch and 
a half above its bifurcation, 
and supplies the lower half 
of the largfe intestine. Con- 
tinned under the name of the 
superior hemorrhoidal artery. 

Fig. 92. -Iliac and Femoral also supplies the rectum. 
2, common iliac artery ; 4, external iliac ; 8, . . 

femoral artery. Poupart's ligament, which -•- '^^ renal arteries are 01 
lies between 4 and 8, is removed. ^.^^gg gi^e, in proportion tO 

the bulk of the organs which they supply. They arise from the 
sides of the aorta, about half an inch below the superior mesen- 
teric artery, that of the right side being generally a little lower 

Chap. X.] 



down than that of the left. Each is directed outwards, so as to 
form nearly a right angle with the aorta. Before reaching the 
kidney, each artery divides into four or five branches. 

The ovarian arteries, corresponding to the spermatic arteries in 
the male, arise close together from the front of the aorta, a little 
below the renal arteries. They supply the ovaries, and, joined 
to the uterine artery, — a branch 
of the internal iliac, — also assist 
in supplying the uterus. During 
pregnancy the ovarian arteries 
become considerably enlarged. 

The common iliac arteries, com- 
mencing at the bifurcation of the 
aorta, pass downwards and out- 
wards for about two inches, and 
then each divides into the internal 
and external iliac arteries. 

The internal iliac artery (whence 
arises the hypogastric in the 
foetus) supplies branches to the 
walls and viscera of the pelvis. 

The external iliac artery forms 
a large continuous trunk, which 
extends downwards in the lower 
limb to just below the knee : it 
is named in successive parts of its 
course external iliac, femoral, and 
popliteal. The external iliac is 
placed within the abdomen, and 
extends from the bifurcation of 
the common iliac to the lower 
border of Poupart's ligament, 
where it enters the thigh and is 
named femoral. 

The femoral artery lies in the upper three-fourths of the 
thigh, its limits being marked above by Poupart's ligament, 
and below by the opening in the great adductor muscle, after 
passing through which the artery receives the name of pop- 
liteal. In the first part of its course the artery lies along the 
middle of the depression on the inner aspect of the thigh, 

Fig. 93. — View of Popliteal 
Artery. A, biceps muscle; D, D, 
gastrocuemius ; /, popliteal artery. 



[Chap. X. 

I— 1 

known as Scarpa's triangle. In this situation the beating of 

the artery may be felt, and the circulation through the vessel 

may be most easily controlled by pressure. 
The popliteal artery, 
continuous with the fem- 
oral, is placed at the back 
of the knee ; just below 
the knee joint it divides 
into the anterior and 
posterior tibial arteries. 

The posterior tibial ar- 
tery lies along the back 
of the leg, and extends 
from the bifurcation of 
the popliteal to the 
ankle, where it divides fflffiii'ji^^'l'i 

into the internal and iSUm wiM''i- 
external plantar arteries. 
About an inch below 
the bifurcation of the 
popliteal, the posterior 
tibial gives off a large 
branch, the peroneal ar- 

The anterior tibial ar- 
tery, the smaller of the 
two divisions of the 
popliteal trunk, extends 
along the front of the 
leg to the bend of the 
ankle, whence it is pro- 
longed into the foot 
under the name of the 
dorsal artery. This 

Fig. 94. — Deep view of unites with the external 
and internal plantar ar- 

THK Arteries of the back 
OF THE Leg. 1, popliteal 
artery; 6, division of pop- tcrics to form the plan 

liteal into anterior and pos- ^ | j^- j^ supplies dorsal artery, 

tenor tibial arteries ; S, pos- ^^ •' 

terior tibial ; 9, peroneal. blood to the f OOt.-^ 

Fig. 95. — Anterior vie\iv 
OF Arteries of the Leg 
4, anterior tibial artery; 9 

1 Drawing an outline of the aorta with its branches as an arterial tree will 
greatly aid the student in mastering the arterial distribution. 

Chap. X.] 



Venous return. — The arteries begin as large trunks, which 
gradually become smaller and smaller until they end in the 
small capillary tubes, while the veins begin as small branches 
which at first are scarcely distinguishable from the capillaries. 
These small branches, receiving the blood from the capillaries 
throughout the body, unite to form 
larger vessels, and end at last by 
pouring their contents into the 
right auricle of the heart through 
two large trunks-, the superior vena 
cava and the inferior vena cava. 
The veins, however, which bring 
back the blood from the stomach, 
intestines, spleen, and pancreas, 
do not take the blood di recti 3^ to 
the heart, they first join to form 
a large trunk, — the portal vein, 
— and carry this blood to the 
liver. When the portal vein enters 
the liver, it breaks up into cap- 
illaries, which, after branching 
throughout the liver substance, 
unite to form the hepatic veins: 
by them the blood is conveyed 
into the inferior vena cava. This 
constitutes what is called the 
portal circulation, and is the only 
example in the body of a vein 
breaking up into capillaries. 

The veins consist of a super- 
ficial and a deep set, the former 
running immediately beneath the 

skin and hence named subcuta- Fig.96.— Arteries of the Foot. 

neOUS, the latter usually aCCOm- i' anterior tibial artery; 6, 7, 8, 

'' branches of dorsal artery. 

panying the arteries and named 

vence comites. These two sets of veins have very frequent com- 
munications with each other, and the anastomoses of veins 
are always more numerous than those of arteries. 

The systemic veins — that is, all the veins of the body with 
the exception of the pulmonary and portal veins — are naturally 
divided into two groups. 



[Chap. X. 

I. Those from which the blood is carried to the heart by the 
superior vena cava, viz. the veins of the head and neck and 

upper limbs, together with those of 
the spine and a part of the walls of 
the thorax and abdomen. In this 
group we may include the veins of 
the heart, which, however, pass directly 
into the right auricle without entering 
the superior vena cava. 

II. Those from which the blood is 
caiTied to the heart by the inferior vena 
cava ; viz. the veins of the lower limbs, 
the lower part of the trunk, and the 
abdominal viscera. 

1. The blood returning from the 
head and neck flows on each side into 
two principal veins, the external and 
internal jugular. 

The external jugular commences near 
the angle of the jaw by the union of 
two smaller veins, and descends almost 
vertically in the neck to its termination 
in the subclavian vein. 

The internal jugular, receiving the 
blood from the cranial cavity, descends 
the neck close to the outer side of the 
internal and common carotid arteries. 
It unites at a right angle with the 
subclavian to form the innominate vein.^ 

The blood from the upper limbs is 
returned by a superficial and deep set 
of veins. The superficial are much 
larger than the deep, and take a greater 

Fia. 97. — Sketch of the 
PRINCIPAL Venous Trunks. 
1, superior vena cava; 2, in- 
ferior vena cava ; .'5, right sub- 
clavian and innominate veins; 
4, left subclavian and innomi- 
nate veins ; 5, 5, right and left 
internal jugular veins; 8, right 
azygos vein ; 10, left azygos 
vein ; 13, 13, common iliac veins ; 
14, 14, sacral veins. 

1 Note on Venous Circulation of the 
Skull. — The blood from the skull is returned 
from the smaller veins to the internal jugular 
veins by channels which are not strictly veins, 
but sinuses. These sinuses are spaces left be- 
tween the layers of the dura mater, and are lined 
by a continuation of the lining membrane of the 

Chap. X.] 



share in returning the blood, especially from the distal portion 
of the limb. The deep veins accompany the arteries, and are 
called by the same names. Both 
sets are provided with valves, and 
terminate in the subclavian vein. 

The blood from the spine, walls 
of thorax, and abdomen is chiefly 
returned by the right and left azygos 
veins, which are longitudinal vessels 
resting against the thoracic portion 
of the spinal column. They com- 
municate below with the inferior 
vena cava, and terminate above in the 
superior vena cava : they thus form a 
supplementary channel by which blood 
can be conveyed from the lower part 
of the body to the heart in case of 
obstruction in the inferior vena cava. 

The innominate veins, commencing 
on each side by the union of the sub- 
clavian and internal jugular, behind 
the inner end of the clavicle, transmit 
the blood returning from the head 
and neck, the upper limbs, and a 
part of the thoracic wall ; they end 
below by uniting to form the superior 
vena cava. Both innominate veins 
are joined by many side tributaries : 
they also receive, at the junction of 
the subclavian and internal jugular, 
the lymph ; on the left side from the 
thoracic duct, and on the right from 
the riglit lymphatic duct. 

The superior or descending vena cava 

/. 11 ,, . p.i •1. Fig. 98. — Superficial veins 

is formed by the union of tlie right of Lower Extremity. -l, veins 

and left innominate veins. It is about of the foot; 2, internal saphenous 

,, • 1 1 1 • . .1 vein: .", superficial veins of calf ; 

three inches long, and opens into the 4, superficial veins of thigh, 
right auricle, opposite the third rib. 

II. The blood from the lower limbs is also returned by a 
superficial and deep set of veins. They are more abundantly 


supplied with valves than the veins of the upper limbs. The 
deep veins accompany the arteries. The two largest superficial 
veins are the internal or long saphenous, and the external or short 
saphenous vein. The internal saphenous extends from the ankle 
to within an inch and a half of Poupart's ligament. It lies 
along the inner side of the leg and thigh, and terminates in the 
femoral vein. The external saphenous arises from the sole of 
the foot, and, passing up the back of the leg, ends in the deep 

Both the deep and superficial veins of the lower limbs pour 
their contents into the external iliac. The blood is returned 
from the pelvis by the internal iliac veins, which, uniting with 
the external iliac, form the two common iliac veins. They 
extend from the base of the sacrum to the fourth lumbar 
vertebra, and then the two common iliacs unite to form the 
inferior vena cava. 

The inferior or ascending vena cava returns the blood from 
the lower limbs, pelvis, and abdomen. It begins at the junction 
of the two common iliacs, and thence ascends along the right 
side of the aorta, perforates the diaphragm, and terminates by 
entering the right auricle of the heart. The inferior vena cava 
receives many tributaries, the chief of which are the lumbar, 
ovarian, renal, and hepatic veins. 

The pulmonary artery. — The pulmonary artery conveys the 
dark venous blood from the right side of the heart to the 
lungs. The main trunk is a short, wide vessel (diameter 
30 mm.) which arises from the right ventricle and runs for 
a distance of two inches backwards and upwards (vide Fig. 78). 
Between the fifth and sixth dorsal vertebrse, it divides into 
two branches, — the right and left pulmonary arteries, — which 
pass to the right and left lungs. 

The pulmonary veins. — The pulmonary veins convey the red 
arterial blood from the lungs to the left side of the heart. 
They are usually four in number, two from each lung. The 
two left veins frequently terminate in the left auricle by a 
common opening. The pulmonary veins have no valves. 

Chap. X.] 




r R, and L. coronary, 

r R- c. carotid. 
i- I Innominate R. subclavian - ax- 

Arch of Aorta I ,-ii„ , , . , 

\ ^ lUary — brachial. 

L. c. carotid. 

L L. subclavian. 





Common Iliac 

r Intercostal. 
J Pericardial. 
1 Bronchial. 

I CEsophageal. 

f Gastric. 
Coeliac axis j Hepatic. 

^ Splenic. 
Sup. mesenteric. 
Inf. mesenteric. 
. Sacral. 

f Superficial 
Ulnar j palmar 
I- arch. 
Radial paj^^gj, 

I. arch. 

oral — popliteal I Ant. tibial, dorsal. J ^rch. 

I- Int. iliac. 


The veins from the 
head, face, and neck > 
unite to form J 

The deep-seated and 
superficial veins 
from the upper 
limbs unite to form j 

External [the external jugular terminates in sub- 
I clavian veins] and internal jugular veins. 

Right and 
left subcla- 
vian veins. 

The deep-seated and •] 
superficial veins External 
from the lower [ iliacs 
limbs unite to form J 

The veins from pelvis 1 Internal 
unite to form j iHacs 

The internal ju- 
gular unites 
with the sub- 
clavians to 

Right 1 
and left 

•_ y VENA 




. Right and left 1 Inferior vena 
common iliacs / cava. 


The right and left azygos veins connected with the inferior vena cava 
below, and superior vena cava above, form a supplementary channel. 

The veins from stomach, spleen, pancreas, and intestines unite to form 
the portal vein, which breaks up into capillaries in the liver, and is returned 
to the inferior vena cava by the hepatic veins. 



The general circulation of the blood. — At each beat of the heart 
the contraction of the ventricles drives a certain quantity of 
blood, probably amounting to four ounces, with great force into 
the aorta and pulmonary artery. The aorta delivers this sup- 
ply of blood from the left ventricle, through its branches, to the 
capillaries in all parts of the body. In the capillaries, the 
blood is robbed of oxygen and other constituents necessary for 
the life and growth of the tissues, is loaded with carbon diox- 
ide and other waste matters, and is returned by the superior 
and inferior vense cavoe to the right side of the heart. From 
the right side of the heart, the blood is conveyed by the pul- 
monary artery to the capillaries in the lungs,i where it receives 
a fresh supply of oxygen and gives up the carbon dioxide with 
which it has become loaded during its circulation through the 
body. Thus a double circulation is constantly and simultane- 
ously going on, the artery from the left side of the heart send- 
ing the pure oxygenated blood to the general system, and the 
artery from the right side of the heart sending the impure blood 
to the lungs for purification. The more extensive circulation 
is usually called the general or systemic circulation, while the 
lesser circulation is generally known as the pulmonary. 

Some features of the arterial circulation. — The flow of blood 
into the arteries is most distinctly remittent ; sudden, rapid 

1 It is to be observed that the lungs receive blood from two sources. From 
the bronchial arteries (branches of the aorta) they receive arterial blood, by 
means of which the tissues of the lungs are nourished ; and from the pulmonary 
artery they receive venous blood, which, in passing through the lungs, is arte- 
rialized by exposure to the air. 




[Chap. XL 

discharges alternating with relatively long intervals during 
which the arteries receive no blood from the heart. Every time 
the heart beats just as much blood flows from the veins into the 

right auricle as escapes 
from the left ventricle into 
the aorta, but this inflow 
is much slower and takes 
a longer time than the 
discharge from the ven- 

The pulse. — When the 
finger is placed on an ar- 
tery a sense of resistance 
is felt, and this resistance 
seems to be increased at 
intervals, corresponding to 
the heart-beat, the artery 
at each heart-beat being 
felt to rise up or expand 
under the finger. This 
constitutes the pulse ; and, 
in certain arteries which 
lie near the surface, this 
pulse may be seen with the 
eye. When the finger is 
placed on a vein very lit- 
tle resistance is felt ; and, 
under ordinary circum- 
stances, no pulse can be 
perceived by the touch or 
by the eye. 

Fig 99.-DIAGRAM OF Circulation, i.left ^^ g^^^j^ expansion of an 
side of heart; R, right side of heart; a, a, a, ar- _ ••• 

terial system; b, b, capillaries; c, c, c, veins; artery is produced by a 
^^im., alimentary caiial; 7.W., liver; p, portal ,.• r .1 1 . 

vein; //, hepatic vein ; /.j/wpA., lymphatic duct contiacuon OI tne lieaiT, 

and tributaries; Pulni., lungs; Pa, pulmonary the pulsC, aS felt in any 
artery; Pw, pulmonary vein. r- • t 

superficial artery, is a con- 
venient guide for ascertaining the character of the heart's action.^ 

1 The nurse should practice "taking the pulse " in the following arteries : — 
carotid, temporal, radial, dorsalis pedis, 

facial, brachial, femoral, 


The radial artery at the wrist, owing to its accessible situation, 
is usually employed for this purpose. Any variation in the 
frequency, force, or regularity of the heart's action is indicated 
by a corresponding modification of the pulse at the wrist. 

The average frequency of the pulse in man is seventy-two 
beats per minute. This rate may be increased by muscular 
action. Even the variation of muscular effort entailed between 
the standing, sitting, and recumbent positions will make a 
difference in the frequency of the pulse of from eight to ten 
beats per minute. Age has a marked influence in the same 
direction. According to Carpenter, the pulse of the foetus is 
about 140, and that of the newly born infant 130. During the 
first, second, and third years, it gradually falls to 100 ; by the 
fourteenth year to 80 ; and is reduced to the adult standard by 
the twenty-first year. At every age, mental excitement may 
produce a temporary acceleration, varying in degree with the 
peculiarities of the individual. 

As a rule, the rapidity of the heart's action is in inverse ratio 
to its force. A slow pulse, within physiological limits, is 
usually a strong one, and a rapid pulse comparatively feeble. 
The same is true in disturbance of the heart's action in disease ; 
the pulse in fever, or other debilitating affections becoming 
weaker as it grows more rapid. 

Arterial tension. — When an artery is severed, the flow of 
blood from the proximal end (that on the heart side) comes in 
jets corresponding to the heart-beats, though the flow does not 
cease between the beats. The larger the artery, and the nearer 
to the heart, the greater the force with which the blood issues, 
and the more marked the remittance of the flow. 

When a corresponding vein is severed, the flow of blood, 
which is chiefly from the distal end (that away from the heart), 
is not remittent, but continuous ; the blood comes out with 
comparatively little force, and " wells up," rather than '' spurts 

The continuous uninterrupted flow of blood in the veins is 
caused by the elasticity of the arterial walls. On account of 
the small size of the capillaries and small arteries the blood 
meets with a great deal of resistance in passing through them ; 
and, in consequence, the blood cannot get through the capilla- 
ries into the veins so rapidly as it is thrown into the arteries by 


the heart. The whole arterial system, therefore, becomes over- 
distended with blood, and the greater the resistance, the greater 
the pressure on, and distension of, the arterial walls. The fol- 
lowing illustration will explain how the elasticity of the arter- 
ies enables them to deliver the blood in a steady flow to the 
veins through the capillaries. 

If a syringe be fastened to one end of a long piece of elastic 
tubing, and water be pumped through the tubing, it will flow 
from the far end in jerks. But if we stuff a piece of sponge 
into this end of the tubing, or offer in any way resistance to 
the outflow of the water, the tubing will distend, its elasticity 
be brought into play, and the water flow from the end not in 
jerks, but in a stream, which is more and more completely con- 
tinuous the longer and more elastic the tubing. 

Substitute for the syringe the heart, for the sponge the cap- 
illaries and small arteries, for the tubing the whole arterial sys- 
tem, and we have exactly the same result in the living body. 
Through the action of the elastic arterial walls the separate jets 
from the heart are blended into one continuous stream. The 
whole force of each contraction of the heart is not at once 
spent in driving a certain quantity of blood onwards ; a part 
only is thus spent, the rest goes to distend the elastic arteries. 
But during the interval between that beat and the next, the 
distended arteries are narrowing again, by virtue of their elas- 
ticity, and so are pressing the blood on in a steady stream into 
the capillaries with as much force as they were themselves dis- 
tended by the contraction of the heart. 

The degree of tension to which the arterial walls are sub- 
jected depends upon the force of the heart-beat, and upon the 
resistance offered by the smaller arteries, the normal general 
blood pressure being mainly regulated by the " tone " of the 
minute arteries. 

Variations in the capillary circulation. — Most of the changes 
in the capillary circulation are likewise dependent upon the 
condition of the smaller arteries. When under certain nervous 
influences they contract, the blood supply to the capillaries is 
greatly lessened ; when, on the other hand, they dilate, the 
blood supply is greatly increased. The phenomena produced 
by these local variations in the blood supply of certain parts are 
very familiar to us ; the redness of skin produced by an irritat- 


ing application, the blushing or paling of the face from mental 
emotion, the increased flow of blood to the mucous membranes 
during digestion, being all instances of this kind. 

But the condition of the capillary walls themselves also exerts 
an influence upon the capillary circulation. If some trans- 
parent tissue, preferably the web of a frog's foot, be watched 
under the microscope, it will be observed that in the small 
capillaries the corpuscles are pressed through the channel in 
single file, each corpuscle as it passes occupying the whole bore 
of the capillary. In the larger capillaries and smaller arteries 
and veins the red corpuscles run in the middle of the channel, 
forming a coloured core, between which and the sides of the 
vessels is a colourless layer containing no red corpuscles, and 
called the " peripheral zone." In the peripheral zone are fre- 
quently seen white corpuscles, sometimes clinging to the walls 
of the vessel, sometimes rolling slowly along, and in general 
moving irregularly, stopping awhile, and then suddenly moving 
on again. 

These are the phenomena of the normal circulation, but a 
different state of things sets in when the condition of the blood- 
vessels is altered in inflammation. i If an irritant, such as a 
drop of chloroform, be applied to the portion of transparent 
tissue under observation, the following changes may be seen to 
occur : the arteries dilate, the blood flows in greater quantity 
and with more rapidity, the capillaries become filled with cor- 
puscles, and the veins appear enlarged and full. This condition 
of distension may pass away, and the blood-vessels return to 
their normal state, the effect of the irritant having merely pro- 
duced a temporary redness. 

The irritant, however, usually produces a more decided 
change. The white corpuscles begin to gather in the periph- 
eral zones, and this takes place though the vessels still re- 
main dilated and the stream of blood still continues rapid, 
though not so rapid as at first. Each white corpuscle exhibits 
a tendency to stick to the sides of the vessels, and, driven away 
from the arteries by the stronger arterial current, becomes 
lodged in the veins. Since white corpuscles are continually 

1 The following account of the changes occurring in inflammation does not 
strictly belong to a text-book on physiology, but I have ventured to introduce it, 
as especially interesting to nurses, out of " Foster's Physiology." 


arriving on the scene, the inner surface of the veins and cap- 
illaries soon become lined with a layer of these cells. Now, 
though the vessels still remain dilated, the stream of blood 
begins to slacken, and the white corpuscles lying in contact 
with the walls of the vessels are seen to thrust themselves 
through the distended walls into the lymph spaces outside. 
This migration of the white cells is accomplished by means of 
their amoeboid movements. They thrust elongated processes 
through the walls, and then, as these processes increase in size, 
the body of the cell passes through into the enlarged process 
beyond, the perforation appearing to take place in the cement 
substance between the endothelial cells forming the walls of 
the vessels. Through this migration, the lymph spaces around 
the vessels in the inflamed area become crowded with white 
corpuscles. At the same time the lymph not only increases in 
amount, but changes somewhat in its chemical characters : it 
becomes more distinctly and readily coagulable, and is some- 
times spoken of as "exudation fluid." This change of the 
lymph with the increased quantity, together with the dilated 
crowded condition of the blood-vessels, gives rise to the swell- 
ing which is one of the features of inflammation. 

If the inflammation, now passes away, the white corpuscles 
cease to emigrate, cease to stick so steadily to the sides of the 
vessels, the stream of blood quickens again, the vessels regain 
their ordinary caliber, and a normal circulation is re-established. 
But this inflammatory condition, instead of passing off, may go 
on to a further stage ; and, if this is the case, more and more 
white corpuscles, arrested in their passage, crowd and block the 
channels, so that, though the vessels remain dilated, the stream 
becomes slower and slower, until at last it stops altogether, and 
stagnation or " stasis " sets in. Tlie red corpuscles, in this con- 
dition of things, are driven in among the white corpuscles, the 
vessels are filled and distended with a mingled mass of red and 
white corpuscles, and it may now be observed that the red cor- 
puscles also begin to find their way through the distended and 
altered walls of the capillaries into the lymph spaces outside. 
This is called the diapedesis of the red corpuscles. 

This stagnation stage of inflammation may be the beginning 
of further mischief and of death to the inflamed tissue, but it, 
too, may like the earlier stages, pass away. 


General summary of the circulation. — The perfect circulation 
of tlie blood is dependent upon certain factors, the chief of 
which are : (1) the character of the heart-beat ; (2) the con- 
traction and relaxation of the minute arteries ; (3) the elas- 
ticity and extensibility of the arterial walls ; (4) the perfect 
adjustment of the valves. 

The character of the heart-beat is mainly determined by the 
condition of its muscular substance, and any interference with 
the nutrition of the heart leading to degeneration of its mus- 
cular walls very seriously affects the heart's action. 

The contraction and relaxation of the smaller arteries is under 
the influence of the nervous system. The muscular tissue found 
in the walls of these vessels is supplied with non-medullated 
nerve-fibres. Stimulation of one set of these fibres (vaso- 
constrictor) causes contraction of the muscle-fibres and con- 
striction of the arteries ; stimulation of a second set (vaso- 
dilator) causes a relaxation of the muscle-fibres, and dilatation of 
the arteries. The widening and narrowing of these arteries not 
only affects the local circulation in different parts of the body, 
but the amount of resistance they oppose to the arterial impulse 
also influences in some degree the character of the heart-beat. 

The elasticity and extensibility of the arteries change with 
the age of the individual. As we grow older the arterial walls 
grow stiffer and more rigid, and become less well adapted for 
the unceasing work they are called upon to perform. The valves 
also show signs of age as years advance, and even if not injured 
by disease, do not adjust themselves so perfectly as in early life. 

Still, the heart has a marvellous facility for adjusting itself 
to changed conditions, and the circulation of the blood may 
go on for years with the integrity of the vascular mechanism 
greatly impaired. 

FcETAL Circulation. — The peculiarities of the fcetal cir- 
culation, leaving details aside, are : the direct communication 
between the two auricles of the heart through an opening 
called the foramen ovale ; the communication between the pul- 
monary artery and descending portion of the arch of the aorta 
by means of a tube called the ductus arteriosus ; and the com- 
munication between the placenta and the foetus by means of 
the umbilical cord. 

The arterial blood for the nutrition of the foetus is carried from 


the placenta along the umbilical cord by the umbilical vein. 
Entering the foetus at the umbilicus the blood passes upwards 
to the liver and is conveyed into the inferior vena cava in two 
different ways. The larger quantity first enters the liver, and 
alone, or in conjunction with the blood from the portal vein, 
ramifies through the liver before entering the inferior vena 
cava by means of the hepatic veins. The smaller quantity of 
blood passes directly from the umbilical vein into the inferior 
vena cava by a tube called the ductus venosus. 

In the inferior vena cava the blood from the placenta becomes 
mixed with the blood returning from the lower extremities of 
the foetus. It enters the right auricle and guided by a valve, 
the Eustachian valve, passes through the foramen ovale into the 
left auricle. In the left auricle it mixes with a small quan- 
tit}^ of blood returned from the lungs by the pulmonary veins. 
From the left auricle the blood passes into the left ventricle, 
and is distributed by the aorta almost entirely to the upper 
extremities. Returned from the upper extremities by the su- 
perior vena cava the blood enters the right auricle and, passing 
over the Eustachian valve, descends into the right ventricle, 
and from the right ventricle into the pulmonary artery. As 
the lungs in the foetus are solid, they require very little blood, 
and the greater part of the blood passes through the ductus 
arteriosus into the descending aorta, where, mixing with the 
blood delivered to the aorta b}^ the left ventricle, it descends 
to supply the lower extremities of the foetus, the chief portion 
of this blood, however, being carried back to the placenta by 
the two umbilical arteries. 

From this description of the foetal circulation, it will be seen : — 

1. That the placenta serves the double purpose of a respi- 
ratory and nutritive organ, receiving the venous blood from 
the foetus, and returning it again charged with oxygen and 
additional nutritive material. 

2. That the greater part of the blood traverses the liver 
before entering the inferior vena cava ; hence the large size of 
this organ at birth. 

3. That the blood from the placenta passes almost directly 
into the arch of the aorta, and is distributed by its branches to 
the head and upper extremities ; hence the large size and per- 
fect development of those parts at birth. 

Plate VI. — Plan of F<i;tal Circulation. In this plan, the figured arrows rep- 
resent the kind of blood, as -well as the direction -which it takes in the vessels. Thus, 
arterial blood is iigured ; venous blood ; mixed (arterial and venous) 



4. That the blood in the descending aorta is chiefly derived 
from that which has already circulated in the upper extremities, 
and, mixed with only a small quantity from the left ventricle, 
is distributed to the lower extremities ; hence the small size and 
imperfect development of these parts at birth. 

Development of blood-vessels and corpuscles. — The blood-vessels and 
red corpuscles are formed very early in the embryo. They are developed in 
that portion of the primitive tissue called the mesoblast. The cells which 
are to form the vessels become extended into processes of varying length, 
"which grow out from the cells in two or more directions. The cells become 

Fig. 100. — Isolated Capillary Network formed by the Junction of 
Several Hollowed-out Cells, and containing Coloured Blood-corpuscles 
IN A Clear Fluid, p, p, pointed cell-processes extending in different directions 
for union with neighbouring capillaries. 

united with one another, either directly or by the junction of their processes, 
so that an irregular network is thus formed. Meanwhile the nuclei in the 
cells multiply, and each nucleus surrounds itself with a small amount of 
cell protoplasm. The corpuscles thus formed acquire a reddish colour, and 
the protoplasmic network in which they lie becomes hollowed out into a 
system of branched canals containing fluid, in which the nucleated coloured 
corpuscles float. The protoplasmic walls of the vessels gradually change 
into the flattened cells which compose the wall of the capillaries, and which 
form the lining membrane of the arteries and veins. The remaining coats 
of the larger vessels are developed later from other cells which apply them- 
selves to the exterior of these tubes. 

The first white corpuscles do not appear in the vessels so early as the 
coloured ones. /They probably occur in the beginning as free cells and 
wander in fronvthe outside. 

The new vessels which form in the healing of wounds and in the restora- 
tion of lost parts are produced by a process which is essentially the same as 
above described. Blood-corpuscles, however, are not produced within them, 
and it is stUl a matter of doubt as to where and how the red corpuscles 
originate after birth. The white corpuscles are undoubtedly produced to a 
large extent in the lymphatic nodes and other lymphoid structures. 




The lymphatics. — In addition to the blood-vessels, which form 
a continuous series of tubes for the passage of the blood, there 
is another system of vessels in the body, which arise in the 
different tissues, and pour their contents into the great veins 
near the heart. The fluid which these vessels contain is ab- 
sorbed from the tissues, and is called, from its transparent 
watery appearance, " lymph " (lympha^ water), while the ves- 
sels themselves are known as lymphatics. 

The lymphatics may be divided into two sets : the lacteals, 
which take up the milk-like fluid, called chyle, from the intes- 
tines and carry it to the thoracic duct ; and the lymphatics 
proper, which drain off the lymph from all parts of the body 
and return it to the blood through the thoracic and right lym- 
phatic ducts. These two sets of vessels, however, are alike in 
structure, and will be considered together under the general 
name of lymphatics. 

The lymphatics are found in nearly all the tissues that are 
supplied with blood. The larger trunks usually accompany the 
deep-seated blood-vessels, and the smaller vessels form networks 
in all parts of the body where the extensively distributed and 
penetrative connective tissue is found. 

The lymphatics have their origin in the connective tissue. 
They may be said to begin as irregularly shaped or tubular 
spaces in the areolae, and are distinguished from the lymph 
spaces in the tissue outside by being lined with a single layer 
of flat, transparent endotheloid cells having a peculiar den- 
tated outline, by means of which they are readily recognized. 




[Chap. XII. 

These united lympli vessels form very irregular labyrinths, 
communicate freely with one another, and are altogether wider 
than the blood capillaries. Tliey form the link between the 
lymph in the tissues outside of themselves and the regular 
lymphatic vessels into which tliey open.^ 

Fia. 101. — A Small Portion of a Lymphatic Plexus. Magnified 110 diam- 
eters. (Ranvier.) L, lymphatic vessel ■with characteristic endothelium; C, cell 
spaces of the connective tissue abutting here and there against the lymphatics. 

In structure, the larger lymphatic vessels closely resemble 
the veins, except that their walls are somewhat thinner and 
more transparent, and are more abundantly supplied with 
valves. The valves are constructed and arranged in the same 
fashion as those of the veins, but follow one another at such 
short intervals, that, when distended, they give the vessel a 
beaded or jointed appearance. They are usually wanting in 
the smaller networks. The valves allow the passage of mate- 
rial from the smaller to the larger lymphatics, and from these 
into the veins, and obstruct the flow of anything in the oppo- 
site direction. The lymphatics do not carry to the tissues. 
Their office is to carry away from the tissues into the veins all 
the material the tissues do not need. 

1 The serous cavities may be regarded as expanded lymph spaces, as they 
open by means of their stomata into the lymphatics, and the fluid v^'hich 
moistens their surfaces is really lympb and not serum. 


The lymphatics, having attained a certain size, do not unite 
into larger and larger trunks, but continue of the same diameter 
until they finally enter two trunks or ducts through which their 
contents are poured into the veins. The lymphatics from the 
right arm, and right side of the head, neck, and upper part of 
the trunk, enter the right lymphatic duct. The vessels from 
the rest of the body, including the lacteals, or lymphatics of the 
intestines, enter the thoracic duct. As we have stated else- 
where (page 127), these ducts pour their contents into the blood 
at the juhction of the internal jugular and subclavian veins. 

The lymph, like the blood in the veins, is returned from the 
limbs and viscera by a deep and by a superficial set of vessels. 
In their course from origin to termination most of the lym- 
phatics pass through small masses of tissue, called lymphatic 
glands, a description of which will be given later on. 

The thoracic duct. — The thoracic duct, from fifteen to eigh- 
teen inches (381 to 457 mm.) long in the adult, extends from 
the second,lumbar vertebra to the root of the neck. It lies in 
front of the bodies of the vertebriB gradually inclining towards 
the left until, when on a level with the seventh cervical verte- 
bra, it turns outwards and arches downwards and forwards to 
terminate in the angle formed by the junction of ^he left inter- 
nal jugular and subclavian veins. The size is usually compared 
to that of a goose quill. It is dilated below where it receives 
the lymphatics from the lower limits and the chyle from the 
lacteals, the dilatation being known as the receptaculum chi/li, 
receptacle of the chyle. The duct is provided with valves, 
and in other respects closely resembles the larger lymphatics 
in structure. It is often alternately contracted and enlarged 
at irregular intervals. 

The right lymphatic duct is a short vessel usually from a quar- 
ter to half an inch (6.3 to 12.7 mm.) in length. It pours its 
contents into the blood at the junction of the right internal 
jugular and subclavian veins. 

The lymph. — The lymph is blood minus certain constituents. 
When examined with the microscope, it is seen to consist of a 
clear liquid with corpuscles floating in it. The liquid part 
resembles tlie plasma of tlie blood in its composition, except 
that it contains relatively more water and less solids. It clots 
when removed from the body, though not so firmly as the 


blood. The lymph corpuscles, usually called leucocytes, agree 
in their characters with the white corpuscles of the blood. 
They vary in number in different parts, being more numerous 
in the lymph which has passed through the lymphatic glands 
than in that which enters these bodies, thus indicating the lym- 
phatic glands as a source of these corpuscles. 

The chyle in the lacteals during digestion has a white aspect 
dependent upon the fatty particles absorbed from the food, and 
suspended in it like oil globules in milk. After fasting the 
lacteals contain lymph which differs very little from the lymph 
found in the ordinary lymphatics. 

The lymph, broadly speaking, is blood minus its red corpuscles. 
The chyle is lymph plus a very large quantity of minutely 
divided fat. 

Movements of the lymph. — The onward progress of the lymph 
from the tissues to the veins is maintained chiefly by three 
things. (1) The difference of the pressure upon the lymph in 
the tissues, and the pressure in the large veins of the neck. As 
we have already seen in our last chapter the pressure exerted 
upon the blood in the capillaries is greater than that exerted 
upon the blood in the veins. This pressure in the smaller blood- 
vessels is communicated through the blood-plasma to the lymph, 
and thus, though the lymph is not subjected to the same amount 
of pressure as the blood in the capillaries, it still stands at a 
higher pressure than the blood in the veins. We may consider 
the lymphatics to form a system of vessels leading from a region 
of higher pressure, viz. the lymph-spaces of the tissues, to a 
region of lower pressure, viz. the interior of the large veins of 
the neck. (2) On account of the numerous valves in the 
lymphatics every pressure upon the tissues in which they lie 
will, by compressing the vessels, cause an outward flow of their 
contents. Active muscular exercise and the manipulation of 
the tissues, as practised in massage, markedly affect the lymph 
flow. (3) During each inspiration the pressure on the thoracic 
duct is less than on the lymphatics outside the thorax, and the 
lymph is accordingly "sucked" into the duct. During the 
succeeding expiration the pressure on the thoracic duct is in- 
creased, and some of its contents, prevented by the valve from 
escaping below, are pressed out into the veins. 

The lymph in the various lymph-spaces of the body varies in 


amount from time to time, but under normal circumstances, 
never exceeds certain limits. Under abnormal conditions, these 
limits may be exceeded, and the result is known as cedema or 
dropsy. Similar excessive accumulations may also occur in the 
larger lymph-spaces, the serous cavities. 

The possible causes of oedema are, on the one hand, an ob- 
struction to the flow of lymph from the lymph-spaces, and on 
the other hand, an excessive transudation, the lymph gathering 
in the lymph-spaces faster than it can be carried away by a 
normal flow. CEdema is almost always due to the latter cause, 
viz. excessive transudation. 

The inflammatory oedema, due to changes in the walls of the 
blood-vessels, we have already touched on in speaking of the 
capillary circulation. In this kind of oedema the transudation 
is, besides being crowded with migrating corpuscles, more dis- 
tinctly coagulable than ordinary lymph. Allied to this inflam- 
matory cedema is the "effusion," which appears in the serous 
cavities when they are inflamed, as in pleurisy and peritonitis. 

Functions of the lymph. — The lymph derived from the blood 
delivers to the elements of the tissues the material each element 
needs to maintain its functional activity, and returns to the 
blood the products of this activity, which products may be 
simple waste, or matters capable of being made use of by some 
other tissue. There is thus a continual interchange going on 
between the blood and the lymph. How this interchange 
is effected may be partially understood by the following 

If a tumbler be completely divided vertically into two com- 
partments by a moist piece of membrane, and a watery solution 
of common salt be placed in one compartment, and a watery 
solution of sugar in the other, it will be found after a time that 
some of the salt has found its way into the solution of sugar, 
and, vice versa, some of the sugar into the salt solution. Such 
an interchange is said to be due to diffusion ; and if the process 
were allowed to go on for some hours, the same proportion of 
salt and sugar would be found in the solutions on each side 
of the dividing membrane. So in the living body. The lymph, 
originally like the blood-plasma (it is blood-j^lasma forced to 
transude through the capillaries by the pressure of the blood), 
becomes altered by the metabolic changes of the tissues which 



it bathes, and we have two different fluids, separated by the 
moist membrane which forms the walls of the blood-vessels, — 
the lymph in the tissues outside the walls of the capillaries 
and the blood inside the capillary walls, — and the same con- 
ditions may be said to exist as in the salt and sugar solutions 

just spoken of. And now the same 
phenomena take place ; for though 
the pressure is higlier in the blood- 
vessels than in the lymph outside, 
some of tlie constituents of the lymph 
pass into the blood by the process of 

These constituents, which, as we 
cannot too often emphasize, are prod- 
ucts resulting from the activity of 
the tissues, are carried away by the 
blood to other tissues, which will 
either make use of them, or, as in 
the kidneys, take them up to make 
excretory fluids, and so remove them 
from the body. 

In consequence of the different 
wants and wastes of different tissues 
at different times, both the lymph 
and blood must vary in composition 
in different parts of the body. But 
the loss and gain is so fairly bal- 
anced that the average composition 
is pretty constantly maintained. The 
blood, on account of the higher press- 
ure, loses more liquid to the lymph 
than it receives back, but this ex- 

„ ,^„ ^ cess is returned back asrain to the 

Fig. 102. — Lymphatics and i i j i i . 

Lymphatic Glands of Axilla blood by the lymphatics when they 

AND Arm. empty their contents into the veins. 

Lymphatic glands.^ — The lymphatic glands are small, solid 

bodies, placed in the course of the lymphatics through which 

1 Lymph nodes is the more appropriate name for these structures, but the 
term " lymphatic glands " being still so generally used, it has been thought best 
for the present to retain it in the text. 



the contents of most of these vessels have to pass in their prog- 
ress towards the thoracic and right lymphatic ducts. These 
bodies are collected in numbers alongside of the great muscles 
of the neck, and also in the thorax and abdomen, especially in 
the mesentery, where they are called the mesenteric glands, and 
alongside of the aorta, vena cava inferior, and the iliac vessels. 
A few, usually of small size, are found on the external parts of 
the head, and considerable groups are situated in the axilla, 
and also in the groin where they receive the name of inguinal 
glands. Some three or four lie on the popliteal vessels, and 
usually one is placed a little below the knee, but none farther 
down. In the arm they are found as low as the elbow joint. 

The size of the lymphatic glands is very various, some being 
not much larger than a hemp seed, and others as large as an al- 
mond, or even larger than this. In shape, they are usually oval. 

A lymphatic gland is covered by an envelope, or capsule, of 
connective and muscular tissue. This capsule sends fibrous 

Fio. 103. — Diagrammatic Section of Lymphatic Gland. (Sharpey.) a.L, 
afferent lymphatic: e.I.. efferent lymphatic; c, capsule, or envelope; </-, trabeculse ; 
^5, lymph-sinus; l.h, pulpy substance of gland. 

bands (trahec\dce) into the substance of the gland, dividing the 
exterior portion into more or less regular compartments, and 
the interior into irregular labyrinths. This framework is occu- 



[Chap. XII. 

pied by reticular or lymphoid tissue,^ the fine meshes of which 
are filled with leucocytes. Between this pulpy substance of the 
gland and the skeleton framework there is a narrow space (left 
white in the diagram) which looks as if the pulp had originally 
filled the framework and then shrunk away slightly on all sides. 
The spaces thus left form channels for the passage of the lymph, 
which, entering the more convex surface by afferent vessels, 
issues, after circulating through the gland, by efferent vessels 
below. In its passage through the gland the lymph takes up 
fresh leucocytes, which are continually multiplying by cell 
division in the glandular substance. The lymphatic glands are 
plentifully supplied with blood. 

Solitary follicles and Peyer's patches. — Closely connected with 
the lymphatic vessels in the intestines are small, rounded bodies 

Fig. 104. — Vertical Section of a Portion of a Peter's Patch, with Lac- 
teal Vessels Injected, a, villi, with their lacteals coloured black ; d, surface of 
rounded follicle, or solitary gland ; e, central part; /, ff, h, i, and k, lymph-channels, 
or lacteal vessels, coloured black. 

of the size of a small pin's head, called solitary glands or follicles. 
These bodies consist of a rounded mass of fine lymphoid tissue, 
the meshes of which are crowded with leucocytes. Into this 
mass of tissue one or more small arteries enter and form a 

1 Reticular or lymphoid tissue is that variety of connective tissue in which 
the branched connective tissue cells unite to form delicate networks. The 
meshes of the network are occupied by fluid in which the leucocytes often, in 
large numbers, wander to and fro. 


capillary network, from which the blood is carried away by one 
or more small veins. Surrounding the mass are lymph channels 
which are continuous with the lymphatic vessels in the tissue 

A Peyer's patch, or " agminated gland," as it is often called, is 
simply a collection of these follicles. A well-formed Peyer's 
patch consists of fifty or more of these solitary follicles, ar- 
ranged in a single layer, close under the epithelium of the 
intestinal mucous membrane, and stretching well down into 
the tissue beneath. These patches are circular or oval in shape, 
and from twenty to thirty in number. They are largest and 
most numerous in the portion of the intestine called the ileum. 
They increase in size during digestion. 

The tonsils are two thick masses of lymphoid tissue, placed 
one on each side of the fauces or throat, into which they pro- 
ject. They are covered by stratified epithelium, and their sur- 
faces are pitted with apertures which lead into recesses or crypts 
in the substance of the tissue. 

The spleen. — The spleen differs in many important particu- 
lars from lymphatic glands, but may be conveniently studied in 
conjunction with them, as it resembles these glands in structure, 
and is possibly connected functionally with the blood. 

Like the lymphatic glands, the spleen is covered by a fibrous 
and muscular capsule which sends fibrous bands to form a net- 
work in the interior of the oraran. In the meshes of the fibrous 
framework lies a soft pulpy substance containing a large 
amount of blood, and, therefore, of a deep red colour. This 
soft, red pulp is dotted with whitish specks, which are small 
masses of lymphoid tissue, and are called the Malpighian cor- 
puscles of the spleen. 

The blood supplied to the spleen appears to escape from the 
minute subdivisions of the arteries into the red pulp before 
entering the exceedingly thin-walled veins by which it is con- 
veyed from the gland. The pulp contains numerous red cor- 
puscles, and many bodies which appear to be red corpuscles in 
process of decay or destruction, and it is surmised that the red 
corpuscles are in some way destroyed, and that additional white 
corpuscles are formed, within the spleen. 

The spleen is covered by a portion of the peritoneum, the 
serous membrane covering the viscera of the abdomen, and 


lies upon the left side of the stomach, in tlie abdominal cavity. 
It is an elongated, flat body, varying greatly in size at different 
periods of life. The size is increased during and after diges- 
tion, and is always large in well-fed, and small in starved, 
animals. In certain diseases, and more especially in typhoid 
and malaria, a temporary enlargement takes place. In pro- 
longed or chronic malaria, a permanent enlargement of the 
spleen occurs, and forms the so-called "ague cake." 



The respiratory apparatus. — Respiration is the main process 
by means of which the body is supplied with oxygen and re- 
lieved of carbon dioxide. 

A respiratory apparatus consists essentially of a moist and per- 
meable membrane, with blood-vessels containing carbon dioxide 
on one side, and air or fluid containing oxygen on the other. 
In most aquatic animals, the respiratory organs are external in 
the form of gills ; in terrestrial or air-breathing animals, the 
respirator}^ organs are situated internally under the form of 
lungs, and are placed in communication with the external air 
by a tube or windpipe. 

In man, the respiratory apparatus may be conveniently di- 
vided into the larynx, trachea, and lungs. 

The larynx. — The larynx is situated between the base of the 
tongue and the top of the trachea, in the upper and front part 
of the neck. Above and behind lies the pharynx, which opens 
into the oesophagus or gullet, and on either side of it lie the great 
vessels of the neck. 

The larynx is made up of nine pieces of cartilage, united 
together by ligaments, and moved by numerous muscles. It is 
lined throughout by mucous membrane,^ which is continuous 
abovf with that lining the pharynx, and below with that lining 
the trachea. In form, the larynx is narrow and rounded below 

^ Mucous membranes resemble the skin in structure, and may be said to 
form an internal skin for the cavities of the body which open exteriorly. They 
always have a basis of connective tissue, are lined with epithelium, and secrete 
a sticky substance called mucus. For a further description, see page 166. 




[Chap. XIII. 

where it blends with the trachea, but broad above, and shaped 
somewhat like a triangular box, with flat sides and prominent 
ridge in front. This prominence, popularly called " Adam's 
apple," is formed by the union of the two largest pieces of 
cartilage (the thyroid) of which the larynx is composed. 

Across the middle of the larynx is a transverse partition, 

formed by two folds of the lining 
mucous membrane, stretching from 
side to side, but not quite meeting 
in the middle line. They thus 
leave in the middle line a chink or 
slit, running from front to back, 
called the glottis or rima glottidis. 
Imbedded in the mucous mem- 
branes at the edges of the slit are 
fibrous and elastic ligaments, which 
strengthen the edges of the glottis 
and give them elasticity. These 
ligamentous bands, covered with 
the mucous membrane, are firmly 
attached at either end to the car- 
tilages of the larynx, and are 
called the vocal cords. The space 
left between their edges, the glottis, 
varies in shape and size, according 
to the action of the muscles upon 
the laryngeal walls. When the 
MENT OF Gullet and Larynx, as larynx is at rest during quiet 

EXPOSED BY A Section A LITTLE TO , , . , 1 ,,••», 1 1 

THE Left OF THE Median Plane OF breathmg, the glottlS IS V-shaped; 
THE Head, a, vertebnu; 6, gullet; during a deep inspiration, it be- 

c, trachea; d, larynx; e, epiglottis; " i -i n • 

/, soft palate; g, opening of Eus- comes almost round; wJnle, during 
tachian tube; k, tongue; I, hard ^j-^g production of a high note, the 

palate ; o, p, q, inferior turbinate i <• i ^ 

bones of left nasal chamber. edges of the cords approximate so 

closely as to leave scarcely any 
opening at all. The glottis is protected by a leaf-shaped lid of 
fibro-cartilage, called the epiglottis, which shuts down upon the 
opening during the passage of food or other matters into the 

The vocal cords produce the voice. A blast of air, driven by 
an expiratory movement out of the lungs, throws the two 

— The Mouth, Nose, and 
WITH THE Commence- 

Chap. XIII.] 



elastic cords into vibrations. These impart their vibrations to 
the column of air above them, and so give rise to the sound 
which we call the voice. 

The larynx is placed in communication with the external air 
by two channels : the one, supplied by the nasal passages, is 
always open ; the other, furnished by the mouth, can be opened 
and closed at will. 
One advantage of this 
arrangement is, that 
when exposed to a 
very cold temperature, 
we can close our 
mouths and breathe 
through the nasal pas- 
sages, which, being nar- 
row, thickly lined, and 
freely supplied with 
blood - vessels, warm 
the air before it reaches 
the lungs. 

The trachea. — The 
trachea or windpipe is 
a fibrous and muscu- 
lar tube, the walls of 
which are strengthened 
and rendered more 
rigid by hoops of car- Fig. lUU. — The Larynx as seen by Means of 
tilace embedded in the ^^^ Laryngoscope in Different Conditions 
* . of the Glottis. A, while singing a high note ; B, 

llbrOUS tissue. ihese in qniet breathing; C, during a deep inspiration. 
hoODS are C-shaned ^' ^^^^ "^ tongue ; e, upper free edge of epiglottis ; 
■'■, . ^'> cushion of the epiglottis; p/i, part of anterior 

and incomplete behind, wall of pharynx; cv, the true vocal cords; cvs, the 
the cartilaginous rings ^^^^^^^cal cords; rr, the trachea with its rings; b, 
o o the two bronchi at their commencement. 

being completed by 

bands of plain muscular tissue where the trachea comes in con- 
tact with the oesophagus. Like the larynx it is lined by mucous 
membrane, and has a ciliated epithelium upon its inner surface. 
The mucous membrane, which also extends into the bronchial 
tubes, keeps the internal surface of the air passages free from 
impurities ; the sticky mucus entangles particles of dust and 
other matters breathed in with the air, and the incessant 



movements of the cilia continually sweep this dirt-laden 
mucus upwards and outwards. 

The trachea measures about four and a half inches (114 mm.) 

Corn II 

iXG. 107. — Front View of Cartilages of Larynx. Trachea and bronchi. 

in length, and three-quarters of an inch (19 ram.) from side to 
side. It extends down into the thorax from the lower part of 
the larynx to opposite the third dorsal vertebra, where it divides 
into two tubes, — the two bronchi, — one for each lung. 

Chap. XIIL] 



The lungs. — The lungs consist of the bronchial tubes and 
their terminal dilatations, numerous blood-vessels, lympliatics, 
and nerves, and an abundance of fine, elastic, connective tissue, 
binding all together. 

The two bronchi, into which the trachea divides, enter the 
right and left lung respectively, and then break up into a great 
number of smaller branches which are called the bronchial 
tubes. The two bronchi resemble the trachea in structure ; but 
as the bronchial tubes divide and subdivide their walls become 
thinner, the small plates of cartilage drop off, the fibrous tissue 
disappears, and the finer tubes are composed of only a thin 
layer of muscular and elastic tissue lined by mucous membrane. 
Finally, these finer tubes end in 
dilated cavities, the walls of \yhich, 
consisting of a single layer of flat- 
tened epitheloid cells, surrounded 
by a fine, elastic, connective tissue, 
are exceedingly thin and delicate. 

Immediately beneath the layer of 
flat cells, and lodged in the elastic 
connective tissue, is a very close 
network of capillary blood-vessels ; 
and the air reaching the terminal 
dilatations by the bronchial tubes is 
separated from the blood in the cap- 
illaries by only the thin membranes 
forming their respective walls. 

The terminal dilatations do not end as simple, rounded sacs, 
like children's air-balloons, but each bronchiole ends in an 
enlargement having more or less the shape of a funnel, and 
called an infundihulum. Each of these infundibula is sub- 
divided into secondary chambers or cavities, called alveoli^ the 
walls of which are honey-combed with "bulgings.''^ In this 
way the amount of surface exposed to the air and covered by 
the capillaries is immensely increased. ^ 

Fig. 108. — Two Alveoli of 
THE Lung. Highly magnified. 
6, 6, bulgiugsof the alveoli, a, a. 

1 These protrusions may be illustrated by a pea-pod, the walls of which are 
filled with " bulgings," made by the pressure of the peas. 

2 The pulmonary alveoli are often spoken of under the general name of air- 
sacs, and the " bulgings " are known as air-cells. The term "air-cells," though 
common, is misleading. 



Speaking roughly, the lungs may be said to consist of a film- 
like elastic membrane covered by a close network of blood- 
vessels. The membrane is arranged in the form of irregularly 
dilated pouches at the end of fine tubes. These tubes open into 
larger and larger tubes, and finally into the windpipe, which 
places them in communication with the external air. 

By virtue of their structure, the larger bronchial tubes 
remain permanently open ; the smaller tubes, however, are sub- 

' 6" 

Fig. 109. — Anterior View of Lungs and Heart. 1, heart; 2, inferior vena 
cava; 3, superior vena cava; 4, right innominate vein; 5, left innominate vein; 
6, jugular vein; 7, subclavian vein; 8, arch of aorta; 8', subclaAnan artery; 9, left 
pulmonary artery; 9', 9', carotid artery; 10, trachea; 11, left bronchus; 12, rami' 
fications of right bronchus exposed in upper lobe of right lung ; 13, 14, middle lobe j 
15, lower lobe ; IG, upper lobe of left lung; 17, lower lobe of left lung. 

ject to collapse when empty ; they also may contract under 
certain nervous influences. The terminal dilatations are emi- 
nently elastic and continually expand and contract ; they are 
bathed with lymph, and are always moist. 

The two lungs occupy almost all the cavity of the thorax 
which is not taken up by the heart. The right lung is the 
larger and heavier; it is broader than the left, owing to the 
inclination of the heart to the left side ; it is also shorter by one 


inch, in consequence of the diaphragm ri.sing higher on the 
right side to accommodate the liver. The right lung is divided 
by fissures into three lobes. The left lung is smaller, narrower, 
and longer than the right, and has only two lobes. Each lung 
is enclosed in a serous sac, the pleura, one layer of which is 
closely adherent to the walls of the chest and diaphragm ; the 
other closely covers the lung. The two layers of the pleural 
sacs, moistened by lymph, are normally in close contact ; they 
move easily upon one another, and prevent the friction that 
would otherwise occur between the lungs and the walls of the 
chest with every respiration. 

The pressure of the atmospheric air upon the lungs through 
the air-passages is greater than it can possibly be upon them 
from the outside through the chest walls, on account of the 
resistance which the solid chest walls offer to this pressure ; 
and, ordinarily, it is impossible for the distended lungs to 
pull away the layer of the plural sac which adheres to them 
from the layer which is attached to the chest wall. If, how- 
ever, the chest wall be punctured, the air from the outside 
will rush in, distend the pleura, and, squeezing the air out of 
the air-sacs into the air-passages, cause the lungs to shrivel up 
and collapse. 

Respiration. — The lungs, then, are placed in an air-tight tho- 
rax, which they, together with the heart and great blood-vessels, 
completely fill. By the contraction of certain muscles (see page 
66), the cavity of the thorax is enlarged ; the lungs are cor- 
respondingly distended to fill the enlarged cavity, and, by this 
distension, the air within the air-sacs becomes expanded and 
more rarefied than the air outside. Being thus expanded and 
rarefied, the pressure of the air within the lungs becomes less 
than that of the air outside, and this difference of pressure 
causes the air to rush through the trachea into the lungs, until 
an equilibrium of pressure is established between the air inside 
the lungs and that outside. This constitutes an inspiration. 
Upon the relaxation of the inspiratory muscles, the elasticity 
of the lungs and of the chest walls causes the chest to return to 
its original size, in consequence of which the air within the 
lungs becomes more contracted and denser than the air outside, 
the pressure within becomes greater than the pressure without, 
and the air rushes out of the trachea until equilibrium is once 


more established. This constitutes an expiration. An inspira- 
tion and an expiration make a respiration. 

As in the heart, the auricular systole, the ventricular systole, 
and then a pause, follow in regular order, — so in the lungs, 
the inspiration, the expiration, and then a pause succeed one 
another. Each respiratory act in the adult is ordinarily repeated 
from fifteen to eighteen times per minute. But this rate varies 
under different circumstances, one of the most important of 
which is age. The average rate in the newly born infant has 
been found to be forty-four per minute, and at the age of live 
years, twenty-six per minute. It is reduced between the ages 
of fifteen and twenty to the normal standard. 

A condition of rest or activity readily influences the number 
of respirations per minute. They are always less frequent 
during sleep, and are markedly increased by severe muscular 

Respiration is an involuntary act. It is possible for a short 
time to increase or retard the rate of respiration within certain 
limits by voluntary effort, but this cannot be done continuously. 
If we intentionally arrest the breathing or diminish its fre- 
quency, after a short time the nervous impulse becomes too 
strong to be controlled, and the movements will recommence 
as usual. If, on the other hand, we purposely accelerate res- 
piration to any great degree, the exertion soon becomes too 
fatiguing for continuance, and the movements return to their 
normal standard. 

The nervous impulses which cause the contractions of the 
respiratory muscles arise in the medulla oblongata, travel down 
the spinal cord, and out along the plirenic and intercostal 
nerves. If the portion of the medulla oblongata, where these 
nervous impulses arise, be removed or injured, respiration 
ceases, and death at once ensues. This part of the medulla is 
known as the respiratory centre. 

The effects of respiration upon the air within the lungs. — At 
birth the lungs contain no air. The walls of the air-sacs are in 
close contact, and the walls of the smaller bronchial tubes or 
bronchioles collapsed and toucldng one another. The trachea 
and larger bronchial tubes are open, but contain fluid and not 
air. When the chest expands with the first breath taken, the 
inspired air has to overcome the adhesions existing between 


the walls of the bronchioles and air-sacs. The force of this 
first inspiratory effort, spent in opening out and unfolding, as it 
were, the inner recesses of the lungs, is considerable. In the 
succeeding expiration, most of the air introduced by the first 
inspiration remains in the lungs, succeeding breaths unfold the 
lungs more and more, until finally the air-sacs and bronchioles 
are all opened up and filled with air. The lungs thus once 
filled with air are never completely emptied again until after 

The air remaining in the lungs after expiration is called the 
old or stationary air into which fresh air is introduced with 
every inspiration, the fresh or tidal air, as it is called, giving 
up its oxygen to, and taking carbon dioxide from, the old or 
stationary air. Thus the stationary air transacts the business 
of respiration, receiving, on the one hand, constant supplies of 
oxygen from the tidal air which it delivers to the blood in the 
capillaries on the walls of the air-sacs ; and, on the other hand, 
returning, in exchange to the tidal air, the carbon dioxide it 
has received from the blood in these capillaries. 

In ordinary respiration the lungs are not distended to their 
fullest extent, but by more forcible muscular contraction the 
capacity of the chest can be further enlarged, and a certain 
additional amount of air will rush into the lungs. This addi- 
tional amount is often spoken of as complemental air. In 
laboured breathing the contraction of the respiratory muscles 
not usually brought into play, such as the muscles of the throat 
and nostrils, becomes very marked. 

The entry and exit of the air are accompanied by respiratory 
sounds or murmurs. These murmurs differ as the air passes 
through the trachea, the larger bronchial tubes, and the bron- 
cliioles. They are variously modified in lung disease, and are 
then often spoken of under the name of " rales." 

The effects of respiration upon the air outside the body. — With 
every inspiration a well-grown man takes into his lungs about 
thirty cubic inches (492 cubic centimetres) of air. The air 
he takes in differs from the air he gives out mainly in three 
particulars : — 

1. Whatever the temperature of the external air, the expired 
air is nearly as hot as the blood ; namely, of a temperature 
between 98° and 100° F. (36.7° and 37.8° C). 


2. However dry the external air may be, the expired air is 
quite, or nearly, saturated with moisture. ^ 

3. The expired air contains about four or five per cent less 
oxygen, and about four per cent more carbon dioxide than the 
external air, the quantity of nitrogen suffering but little change. 
Thus : — 

Oxygen. Nitrogen. Carbon Dioxide. 

Inspired air contains . . . 20.81 79.15 0.04 

Expired air contains . . . 16.033 79.587 4.38 


In addition the expired air contains a certain amount of effete 
matter of a highly decomposable and impure character. The 
quantity of water given off in twenty-four hours varies very 
much, but may be taken on the average to be about nine ounces 
(266 cubic centimetres). The quantity of carbon given off at the 
same time is pretty nearly estimated by a piece of pure charcoal 
weighing eight ounces (248 grammes). 

If a man breathing fifteen to sixteen times a minute takes in 
thirty cubic inches (492 cubic centimetres) of air with each 
breath, and exhales the same quantity, it follows that in twenty- 
four hours from three hundred and fifty to four hundred cubic 
feet (9910 to 11,326 cubic decimetres) of air will have passed 
through his lungs. And if such a man be shut up in a close 
room measuring seven feet (2.1 metres) each way, all the air 
in the room will have passed through his lungs in twenty-four 

Since at every breath the external air loses oxygen and gains 
carbon dioxide and other waste and poisonous matters, it is 
imperative that some provision be made for constantly renewing 
the atmospheric surroundings of people in dwelling houses. 
This is accomplished by ventilation, which consists of a system 
of mechanical contrivances, by means of which foul air is con- 
stantly removed and fresh air as constantly supplied. 

The minimum amount of air space every individual should 
have to himself is 800 cubic feet (22,652 cubic decimetres), — 
a room nine feet (2,7 metres) high, wide, and long contains 729 

1 This moisture evaporates from the blood. It is thought by some authorities 
that most of the moisture is collected by the breath from the mucous membrane 
of the respiratory tract. A certain quantity, liowever, evaporates from the 
blood through the walls of the capillaries, and, escaping with the carbon dioxide 
through the membrane of the alveoli, is carried upwards in every expiration. 


cubic feet (20,642 cubic decimetres), — and this space should 
be accessible by direct or indirect channels to the outside air. 

Effects of respiration upon the blood. — While the air in passing 
into and out of the lungs is robbed of a portion of its oxygen 
and loaded with a certain quantity of carbon dioxide, the blood 
as it streams along the pulmonary capillaries is also undergoing 
important changes. As it leaves the right ventricle it is venous 
blood of a dark purple colour ; when it enters the left auricle 
it is arterial blood and of a bright scarlet colour. In passing 
through the capillaries of the body from the left to the right 
side of the heart it is again changed from the arterial to the 
venous condition. The question arises, how is this change of 
colour effected? 

As we have already seen, the blood in the thin-walled, close- 
set pulmonary capillaries is separated from the air in the air- 
sacs by only the moist delicate membranes which form their 
respective walls. By diffusion the oxygen in the air passes 
through these moist membranes into the venous blood in the 
pulmonary capillaries, combines with the reduced haemoglobin 
which has lost its oxygen in the tissues, and turns it into oxy- 
hsemoglobin ; the purple colour shifts immediately into scarlet, 
and the red corpuscles hasten onwards to carry this oxy-hoemo- 
globin to the tissues. Passing from the left ventricle to the 
capillaries in the tissues the oxy-haemoglobin gives up some of its 
oxygen, the colour shifts back again to a purple hue, and the red 
corpuscles return with this reduced haemoglobin to the lungs. 

The oxygen given up by the blood readily combines with the 
unstable chemical compounds of which the tissues are composed. 
In this process, called oxidation} complex bodies are broken up 
into simpler ones, such as carbon dioxide and water, and there 
is thus liberated a great deal of energy which is manifested in 
the increasing of muscular activity, and in the production of 
heat. The carbon dioxide passes by diffusion into the venous 
blood, and is carried by it to the right side of the heart and 
thence to the lungs, a certain quantity, however, escaping from 
the blood through the kidneys and skin. A small and insig- 

1 This process of oxidation may be illustrated by the burning of a fire ; the 
oxygen which is in the air combines with the carbon of the wood, heat and light 
are generated, and oxidized products in the form of carbon dioxide and ashes 


nificant amount of oxygen is introduced into the blood through 
the skin, and, with the food, through the alimentary canal ; but, 
as we have stated in the beginning of this chapter, respiration 
is the main process by means of which the body is supplied with 
oxygen and relieved of carbon dioxide. 

The respiration and circulation are profoundly and intimately 
connected, any change in the blood immediately affecting the 

It would appear that stimulation of the respiratory centre in 
the medulla oblongata depends primarily upon the condition of 
the blood. If the blood is very rich in oxygen the res^Dirations 
are feeble and shallow ; if, on the other hand, the blood is highly 
venous the respirations are deeper and more frequent, and if the 
blood remains venous, gradually become forced and laboured 
until we get the condition called " dyspnoea." Should the blood 
get more and more venous, the impulses generated in the respir- 
atory centre become more and more vehement. These nervous 
impulses, instead of confining themselves to the usual nerves 
distributed to the ordinary respiratory muscles, overflow on to 
other nerves and put into action other muscles until there is 
scarcely a muscle in the body that is not affected. The muscles 
which are thus more and more thrown into action are especially 
those tending to carry out or to assist expiration ; and at last if 
no relief is afforded the violent respiratory movements give way 
to general convulsions of the whole body. By the violence of 
these convulsions the whole nervous system becomes ex- 
hausted, the convulsions soon cease, and death is ushered in 
with a few infrequent and long-drawn breaths. 

It has been surmised that the excitability of the respiratory 
nerve-centre is due to certain chemical substances which act as 
stimulants. AVhen the blood is rich in oxygen this substance is 
oxidized or burned, and removed so fast that it is able to exert 
but little influence on the respiratory nerve-centre ; when, how- 
ever, the blood is poor in oxygen, this substance accumulates 
and the nerve-centre is powerfully stimulated. Thus when the 
blood needs oxygen, the respirations are increased to get, if 
possible, more air into the lungs; if the blood is too rich in 
oxygen, the respirations become abnormally quiet and shallow. 

Modified respiratory movements. — Various emotions may be 
expressed by means of tlie respiratory apparatus. 


Sighing is a deep and long-drawn inspiration, chiefly through 
the nose. 

Yaivning is an inspiration, deeper and longer continued than 
a sigh, drawn through the widely open mouth, and accompanied 
by a peculiar depression of the lower jaw. 

Hiccough is caused by a sudden, inspiratory contraction of the 
diaphragm ; the glottis suddenly closes and cuts off the column 
of air just entering, which, striking upon the closed glottis, 
gives rise to the characteristic sound. 

In sobbing, a series of convulsive inspirations follow each 
other slowly, the glottis is closed, so that little or no air enters 
the chest. 

Coughing consists, in the first place, of a deep and long-drawn 
inspiration by wliich the lungs are well filled with air. This is 
followed by a complete closure of the glottis, and then comes a 
forcible and sudden expiration, in the midst of which the glottis 
suddenly opens, and thus a blast of air is driven through the 
upper respiratory passages. 

In sneezing, the general movement is the same, except that 
the opening from the pharynx into the mouth is closed by the 
contraction of the pillars of the throat and the descent of the soft 
palate, so that the force of the blast is driven entirely through 
the nose. 

Laughing consists essentially in an inspiration, followed by a 
whole series of short spasmodic expirations, the glottis being 
freely open during the whole time, and the vocal cords being 
thrown into characteristic vibrations. 

In crying, the respiratory movements are the same as in 
laughing; the rhythm and the accompanying facial expressions 
are, however, different, though laughing and crying often be- 
come indistinguishable. 



Section I. Preliminary remarks on secreting glands and mucous 

Section II. Food-principles ; proteids, fats, carbo-hydrates, water, saline 
and mineral substances : chemical composition of the body : average compo- 
sition of milk, bread, and meat. Concluding remarks. 

Section I. In our last chapter, we described the methods by- 
means of which the blood is supplied with one of its most vital 
constituents, oxygen. In the next three chapters, we shall con- 
sider how the blood is supplied with those materials through 
the alimentary canal, which it also constantly requires to main- 
tain the life and growth of the body. 

The subject of alimentation, or the process by which the 
body is nourished, naturally falls into three divisions, viz. : — 

(1) Food. 

(2) Digestion. 

(3) Absorption. 

In order, however, to make the subject more intelligible, it 
will be necessary to make a few preliminary remarks upon the 
construction of secreting glands and mucous membranes. 

Secreting glands. — The secreting glands differ from other 
glands, such as the lymphatic glands, the tonsils, Peyer's 
patches, etc., by being always devoted to the function of 
secretion, and by discharging the secretions they form through 
little tubes or ducts which open exteriorly. The lymphatic 
glands and bodies of allied structure are often spoken of as 
ductless glands, in order to distinguish them from these true 
secreting glands provided with ducts. 

A secretion is a substance elaborated from the blood by cell 


Chap. XIV.] 



action, and poured out upon the external or internal surfaces 
of the body. An excretion resembles a secretion, except that 
whereas the secretion is formed to perform some office in the 
Dody, the excretion is formed only to be thrown out of the body. 

Fig. 110. — Diagram showing Various Forms of Secreting Glands. 1, gen- 
eral plan of a secreting membrane; a, epithelial cells; b, basement membrane; 
c, coimective tissue in which lie the blood-vessels (d) ; 2-7, simple and compound 
tubular and saccular glands ; d, duct. 

A secretory apparatus consists essentially of a layer of secret- 
ing cells placed in close communication with a network of blood- 
vessels. The simplest form in which a secretory apparatus 
occurs is in the shape of a plain, smooth surface, composed of 


a single layer of epithelial cells, resting usually on a thin mem- 
brane, on the under surface of which is spread out a close net- 
work of blood-vessels. In order to economize space and to 
provide a more extensive secreting surface, the membrane is 
generally increased by dipping down and forming variously 
shaped depressions or recesses, these depressions or recesses 
being called the secreting glands. 

The secreting glands are of two kinds, simple and compdund. 
The simple glands are generally tubular or saccular cavities, the 
tube in the tubular variety being sometimes so long that it coils 
upon itself, as in the sweat glands of the skin ; they all open 
upon the surface by a single duct. In the compound glands, 
the cavities are subdivided into smaller tubular or saccular 
cavities, opening by small ducts into the main duct which pours . 
the secretion upon the surface. 

However simple or complicated the involuted surface, the 
secreting process is essentially the same ; and in this process 
the nucleated cells play the most important part. These cells 
take into their interior those substances from the blood which 
they require to make the special secretion they are set apart 
to form, converting this selected material into chemical com- 
pounds, which either act as solvents, as in the digestive juices, 
or perform some other office in the body. The secretion the 
cells elaborate escapes from them either by exudation or by the 
bursting and destruction of the cells themselves. Cells filled 
with secreting matter may also be detached and carried out 
entire with the fluid part of the secretion; and, in all cases, 
new cells speedily take the place of those which have served 
their office. The glands are provided with lymphatics, and fine 
nerve fibrils have also been found to terminate in them. That 
they are under the influence of the nervous system is shown by 
the fact that impressions made on the nervous system affect 
the secretions, a familiar instance of which is the flow of saliva 
into the mouth, caused by the sight, or smell, or even the 
thought of food. 

The position and functions of the several glands will be de- 
scribed later in connection with digestion and elimination. 

Mucous membranes. — The mucous membranes, unlike the 
serous membranes, line passages and cavities which communi- 
cate with the exterior. They are all subject to the contact 


of foreign substances introduced into the body, such as air 
and food, and also to the contact of secreted matters ; hence 
their surface is coated over and protected by mucus, a thicker 
and more sticky fluid than the lymph which moistens the 
serous membranes. The mucous membranes of different parts 
are continuous, and they may nearly all be reduced to two 
great divisions ; namely, the gastro-pneumonic and the genito- 

The gastro-pneumonic mucous membrane covers the inside 
of the alimentary canal, the air-passages, and the cavities com- 
municating with tliem. It commences at the edges of the lips 
and nostrils, proceeds through mouth and nose to the throat, 
and thence is continued throughout the entire length of the 
alimentary canal to the anus. At its origin and termination it 
is continuous with the external skin. It also extends through- 
out the windpipe, bronchial tubes, and air-sacs. From the inte- 
rior of the nose the membrane may be said to be prolonged into 
the lachrymal passages, and under the name of conjunctival 
membrane, over the fore part of the ej^eball and inside of the 
eyelids, on the edges of which it again meets with the skin. 
From the upper part of the pharynx a prolongation extends, on 
each side, along the passage to the ear ; and offsets in the ali- 
mentary canal go to line the salivary, pancreatic, and biliary 
ducts, and the gall-bladder. 

The genito -urinary mucous membrane lines the inside of the 
bladder, and the whole urinary tract from the interior of 
the kidneys to the meatus urinarius, or orifice of the ure- 
thra ; it also lines the vagina, uterus, and Fallopian tubes in 
the female. 

The mucous membranes are attached to the parts beneath 
them by areolar tissue, here named " submucous," and which 
differs greatly in quantity as well as in consistency in different 
parts. The connection is in some cases close and firm, as in 
the cavity of the nose. In other instances, especially in cavities 
subject to frequent variations in capacity, like the gullet and 
stomach, it is lax; and when the cavity is narrowed by con- 
traction of its outer coats, the mucous membrane is thrown into 
folds or rugcB which disappear again when the cavity is dis- 
tended. But in certain parts the mucous membrane forms 
permanent folds that cannot be effaced, and which project con- 


spicuously into the cavity which it lines. The best marked 
example of these folds is seen in the small intestine, where 
they are called valvulm conniventes, and which are doubtless 
provided for increasing the amount of absorbing surface for the 
products of digestion. The redness of mucous membranes is 
due to their abundant supply of blood. 

A mucous membrane is composed of a layer of connective 
tissue called the corium, and of a layer of epithelium which 
covers the surface. The epithelium is the most constant part 
of a mucous membrane, being continued over certain parts to 
which the other parts of the membrane cannot be traced. It 
may be scaly and stratified, as in the throat ; columnar, as in 
the intestine ; or ciliated, as in the respiratory tract. The 
mucus which moistens its surface is either derived from little 
glands in the mucous membrane, or from the columnar cells 
which cover the surface. The corium of a mucous membrane 
is composed of either areolar or lymphoid connective tissue. 
It is usually bounded next to the epithelium by a basement 
membrane, and next to the submucous tissue by a thin layer of 
plain muscular tissue termed the muscularis mucosce : this layer 
is not always present. The connective tissue layer varies much 
in structure in different parts ; the lymphoid variety is in cer- 
tain places greatly increased in amount, packed with lymphoid 
cells, and forms the solitary follicles and Peyer's patches de- 
scribed in Chapter XII. 

The small blood-vessels conveying blood to the mucous mem- 
branes divide in the sub-mucous tissue, and send smaller branches 
into the corium, where they form a network of capillaries just 
under the basement membrane. The lymphatics also form net- 
works in the corium and communicate with larger vessels in 
the sub-mucous tissue below. The free surface of the mucous 
membrane is in some parts smooth, but in others is beset with 
little eminences called papillae and villi. 

The papillce are best seen on the tongue ; they are small 
processes of the corium, mostly of a conical shape, containing 
blood-vessels and nerves, and covered with epithelium. 

The villi are most fully developed on the mucous coat of 
the small intestine. Being set close together like the pile 
of velvet, they give a shaggy or villous appearance to the 
membrane. They are little projections of the mucous mem- 

Chap. XIV.J 



brane, covered with epithelium, and containing blood-vessels 
and lacteals, and are favourably arranged for absorbing nutri- 
tive matters from the intestines. 

Section II. Food. — Under the term 
" food " we include all substances, solid or 
liquid, necessary for nutrition. The ques- 
tion at once arises : What are these sub- 
stances, and how are they obtained ? 

If we analyze the food we daily take into 
our mouths and introduce into the aliment- 
ary canal, we find it separable into two 
divisions ; viz. that which is nutritious, 
and that which is innutritions. The nutri- 
tious portion, that which can be digested, 
absorbed, and made use of by the body, 
is generally spoken of under the name 
of food-stuffs or food-principles : the innutri- 
tious portion, usually by far the smaller of 
the two divisions, never enters the body 
at all, properly speaking, but passes through 
the alimentary canal and is excreted in the 
form of feces. 

Food-stuffs are composed mainly of the elementary chemical 
substances, — oxygen, carbon, hydrogen, nitrogen, — and may, 
according to the varying proportions in which these chemical 
elements combine, form five distinct and different classes of 
food-stuffs. These are : — 

Fig. 111. — An Intes- 
tinal Villus. «, a, a, 
columnar epithelium ; 
h, b, capillary network; 
c, c, longitudinal muscle 
fibres ; d, lacteal vessel. 

1. Proteids. 

2. Fats. 

3. Carbo-hydrates. 

4. Water. 

5. Saline or mineral matters. 

Proteids. — Proteids form a large proportion of all living 
bodies, and are an essential part of all living structures. They 
contain on an average in every 100 parts about : — 

Carbon 53 parts 

Hydrogen 7 " 

Oxygen 24 " 

Nitrogen 16 " 


with usually a little sulphur and sometimes a trace of phos- 
phorus and iron. They are the only food-stuffs that contain 
nitrogen in any appreciable quantity, and are sometimes classed 
as " nitrogenous " food-stuffs. Proteids occur in the form of 
albumin in the white of egg (egg-albumin), in milk, in blood 
and lymph (serum-albumin) ; in the form of casein in milk and 
cheese ; of myosin and sy^itonin in muscle ; of vitellin in tlie 
yolk of eggs ; of gluten in flour. Allied to proteids but of 
less nutritive value are the chondrin, obtained from cartilage, 
and the gelatin, obtained from other varieties of connective 
tissue, by boiling. 

All proteids yield peptones very readily at the temperature 
of the body under the action of the acid gastric, and alka- 
line pancreatic juice. These peptones are highly soluble bodies 
and readily absorbed. 

The foods that are most rich in the various forms of proteids 
are meat, milk, eggs, cheese, all kinds of fish, wheat, beans, 
and oatmeal. 

Fats. — Fats are composed of carbon, hydrogen, and oxygen. 
They contain on an average in every 100 parts : — 

Carbon 76.5 parts 

Hydrogen 12 " 

Oxygen 11.5 " 

The most important fats are stearin, palmitin, margarin, and 
olein, which exist in .varying proportions in the fat of animals 
and vegetable oils, and in milk, butter, lard, etc. The brains 
of animals and the yolk of eggs contain a complex phosphor- 
ized fat, called lecithin. Fatty matters are very abundant 
in olives, sweet almonds, chocolate, castor-oil bean, hemp, and 
flaxseed. Most of the fatty substances of food are liquefied 
at the temperature of the body, and are readily oxidized, 
probably on account of the large amount of carbon which 
they contain. 

Carbo-hydrates. — In the carbo-hydrates there is sufficient 
oxygen present to saturate all the hydrogen and to form 
water ; hence their name. In the fats, there is not quite so 
much oxygen as hydrogen ; water is, therefore, not formed 
in them, and in this particular they differ from the carbo- 


The carbo-hydrates contain in every 100 parts about : — 

Carbon 44 parts 

Hydrogen 6 " 

Oxygen 50 " 

The principal carbo-hydrates are starch and sugars. Starch is 
found in wheat, Indian corn, oats, and all grains, in potatoes, 
peas, beans, roots and stems of many plants, and in some fruits. 
In a pure state, it appears as a white powder, as in arrowroot 
and cornstarch. Under the influence of dry heat, starch may 
be converted into a soluble substance, called dextrine; and, 
under the action of certain of the digestive juices, at the tem- 
perature of the body, into sugar. Of sugars there are several 
kinds : cane sugar or sucrose, obtained chiefly from the sugar- 
cane, beet sugar, and maple sugar ; grape sugar or glucose, found 
in grapes, peaches, and other fruits (it is also readily manufac- 
tured from starch); rtialt sugar or maltose, obtained from malt; 
milk sugar or lactose, obtained from milk. 

Carbo-hydrates are readily oxidized ; together with fats, they 
are often classed as " non-nitrogenous " food-stuffs. 

Water is a compound of oxygen and hydrogen, water being 
produced whenever two molecules of hydrogen unite with one 
of oxygen. Next to air, water is the most necessary principle 
of life. It forms about seventy per cent of the entire bodily 
weight. It is an essential constituent of all tlie tissues, as 
well as forming the chief part of all the fluids of the body. 
It acts as a solvent upon various ingredients of the food, lique- 
fying them and rendering them capable of absorption. Most 
of the water of the body is taken into it from without, but it 
is also formed within the body by the union of hydrogen and 
oxygen in the tissues. 

Mineral salts. — The mineral substances chiefly necessary for 
nutrition are : — 

Carbonate J 

- of soda and potash. 

Phosphate! „ ,. , 

^ , ^ 01 lime and magnesia. 

Carbonate J 



[Chap. XIV. 

Of these substances, chloride of soda, sodium chloride or com- 
mon salt, is the most important mineral ingredient of food. It 
is contained in nearly everything we eat, but usually not in 
sufficient quantity to supply all the needs of the body, and we 
therefore add it as a separate article of diet. It is present in 
most of the fluids of the body, notably in the blood. The rest 
of the mineral substances are usually contained in sufficient 
quantity in an ordinary diet, though occasionally it becomes 
necessary to supply them independently. Of all the mineral 
salts, phosphate of lime exists in the largest quantity in the 
body ; it enters largely into the composition of the bones, teeth, 
and cartilages, and gives firmness and solidity to the tissues. 
It is present in very small quantities in the bodily fluids, with 
the exception of the milk, which contains a notable amount of 
phosphate of lime, and which serves for the ossification of the 
growing bones of infants and young children. 

Chemical composition of the body. — Professor Atwater gives 
the following average composition of the body of man, weigh- 
ing 148 pounds : — 

Oxygen 92.4 

Carbon 31.3 

Hydrogen 14.6 

Nitrogen 4.6 , 

Calcium 2.8 

Phosphorus 1.4 

Potassium 34 

Sulphur 24 

Chlorine 12 

Sodium 12 

Magnesium .04 

Iron 02 

Fluorine 02. 

The human body, from a chemical point of view, may be 
regarded as a mixture of three large classes of chemical sub- 
stances ; viz. proteids, fats, and carbo-hydrates associated with 
water and mineral salts. 

In our first chapter we said that protoplasm was the basis of 
the life of the body, and from that point of view we may look 
upon the human body as an assemblage of variously modified 
protoplasm. But it comes to the same thing, for the chemical 




composition of protoplasm, so far as it has been possible to 
analyze it, lias been found to agree closely with that of the 
fully developed organism. 

The processes of nutrition that take place in the cell are 
essentially the same as those which take place in the fully 
developed body. In both cases, non-living chemical substances 
are taken in from without, and converted into material which 
is endowed with that mysterious property we call life. 

To support life, the different food-stuffs must be taken in 
proper proportion; and, in order that all the tissues and fluids 
of the body may continue in good condition and perform their 
functions properly, they must be supplied with all the ingredi- 
ents necessary to their constitution. A man may be starved to 
death at last by depriving him of lime phosphate as surely, 
though not as rapidly, as if he were deprived of albumin or fat. 
Many a patient in less well-instructed times has been slowly 
killed by deprivation of water, or by exclusive feeding on beef- 
teas and jellies. 

Average composition of milk, bread, and meat. — The following 
analyses of the composition of three staple articles of diet — 
milk, bread, and meat — are taken from Dalton. 

Average composition of milk in 100 parts : — 

Water 86.4 

Proteids 4.3 

Sugar 5.2 

Fat 3.7 

Mineral salts .4 

Average composition of wheaten bread in 100 parts : — 

Starchy matters 56.7 

Proteids 7.0 

Fatty matters 1.3 

Mineral salts 1.0 

Water 34.0 

Average composition of beef flesh : — 

Water 77.5 

Proteids 16.0 

Pat 5.0 

Mineral salts 1.5 


Concluding remarks. — The quantity and also the kind of food 
each individual daily requires depends chiefly upon the nature 
and the amount of the work he is called upon to perform, and 
the conditions of the climate in which he lives. Universal 
experience has taught us that the best sustainers of life are 
milk and bread and water, with a certain amount of meat and 
fat. These should form the basis of all our diets, though not 
to the exclusion of other food-stuffs, for it has also been proved 
that a mixed diet is always to be preferred to one that consists 
constantly of the same articles of food. 

To determine the relative digestibility of foods is a very diffi- 
cult matter in view of the individual peculiarities of different 
people. Strawberries may agree perfectly with ninety-nine 
people, and with the hundredth, act as a powerful poison. 
Some persons, as we all know, cannot tolerate milk or eggs, 
and yet, from a chemical point of view, these foods are emi- 
nently suitable articles of diet. 

The best diet is that which contains all the articles of food 
necessary for the wants of the body in proper proportions, which 
is agreeable to the individual, and which gives the minimum 
amount of work to the digestive organs.^ 

Food to be of any use to the body must be digested and 
assimilated. We may partake of an ideal diet and yet remain 
imperfectly nourished, if our digestive organs are out of order, 
or our power to absorb and assimilate digested products in any 
way impaired. In our next chapter we shall describe the ali- 
mentary canal, the accessory digestive organs, and the methods 
by means of which the food is reduced to a condition available 
for the uses of the body. 

1 For valuable information on the relative value of foods and preparation of 
the same for the sick, the student is referred to Boland's " Handbook of Invalid 



The digestive apparatus consists of the alimentary canal, and 
the accessory organs, the teeth, salivary glands, pancreas, and 

Alimentary canal. — The alimentary canal is a musculo-mem- 
branous tube extending from the mouth to the anus. It is 
about six times the length of the bod}^, and the greater part of 
it is coiled up in the cavity of the abdomen. The diameter of 
the tube is by no means uniform, being considerably dilated in 
certain parts of its course. It is composed of three coats from 
the mouth to where it passes through the diaphragm, and of 
four coats in the abdominal cavity. These coats are : (1) the 
mucous, (2) the sub-mucous (both described in the last chapter) ; 
(3) the muscular ; (4) the serous. The muscular coat is com- 
posed for the most part of unstriped muscular fibres, the layers 
of which are disposed in various wa3^s, the most general arrange- 
ment being in a longitudinal and circular direction. By the 
alternate contraction and relaxation of fibres arranged in this 
fashion (the contractions starting from above), the contents of 
the tube are propelled from above downwards. The serous coat 
is derived from the peritoneum, which is the serous membrane 
lining the walls, and covering the viscera, of the abdomen. 

Into the interior of the alimentary canal are poured secre- 
tions from the glands in the mucous membrane with which it is 
lined, and also secretions from the accessory glands, which lie 
outside the canal and are connected with its interior by ducts. 

The alimentary canal for convenience of description may be 
divided into : — 

1 Plate VII. shows relative position of digestive organs in abdominal cavity. 


Plate VII. — Regions of the Abdomen and their Contents (Edge op Costal 
Cartilages in Dotted Outline). 

For convenience of description the abdomen may be artificially divided into nine 
regions by drawing two circular lines round the body parallel tvnth the cartilages of 
the ninth ribs, and the highest point of the crests of the ilia ; and two vertical lines 
from the cartilage of the eighth rib on each side to the centre of Poupart's ligament. 
The viscera contained in these different regions are as follows : — 

Eight Hypochondriac. — 
The right lobe of the liver and 
the gall-bladder, hepatic flexure 
of the colon, and part of the 
right kidney. 

Epigastric Eegion. — The 
middle and pyloric end of the 
stomach, left lobe of the liver, 
the pancreas, the duodenum, 
parts of the kidneys and the 
suprarenal capsules. 

Left Hypochondriac. — The 
splenic end of the stomach, the 
spleen and extremity of the pan- 
creas, the splenic flexure of the 
colon, and part of the left kid- 

Right Lumbar. — Ascend- 
ing colon, part of the right kid- 
ney, and some convolutions of 
the small intestines. 

Eight Inguinal (Iliac). — 
The cajcum, appendix cseci. 

Umbilical Region. — The 
transverse colon, part of the 
great omentum and mesentery, 
transverse of the duode- 
num, and some convolutions of 
the jejunum and ileum, and 
part of both kidneys. 

Hypogastric Region. — Con- 
volutions of the small intes- 
tines, the bladder in children, 
and in adults if distended, and 
the uterus during pregnancy. 

Left Lumbar. — Descending 
colon, part of the omentum, 
part of the left kidney, and 
some convolutions of the small 

Left Inguinal (Iliac). — 
Sigmoid flexure of the colon. 


Chap. XV.] 



Mouth, containing tongue and teeth. 


Small intestine-j Jejunum. 




Mouth or buccal cavity (vide Fig. 113). — The mouth is a nearly 
oval-shaped cavity with a fixed roof and movable floor. It is 
bounded in front by the lips, on the sides by the cheeks, below 
by the tongue, and above by the palate. The palate con- 
sists of a hard portion 
in front formed by 
bone covered by mu- 
cous membrane, and 
of a soft portion be- 
hind containing no 
bone. The hard palate 
forms the partition 
between the mouth 
and nose ; the soft 
palate arches back- 
wards and hangs like 
a curtain between the 
mouth and the phar- 
ynx. Hanging from 
the middle of its lower 
border is a pointed 
portion of the soft pal- 
ate called the uvula ; 

and arching outwards and downwards from the base of the 
uvula on each side to the back of the tongue are two curved 
folds of muscular tissue covered by mucous membrane, called 
the pillars of the fauces. Just before reaching the tongue, 
the two pillars, on either side, are separated by a triangular 
space in which lie the small masses of lymphoid tissue called 
the tonsils. The fauces is the name given to the aper- 

FiG. 112. — The Salivary Glands. 


ture leading from the mouth into the pharyjix or throat 

The mucous membrane lining the mouth contains many 
minute glands which pour their secretion upon its surface, 
but the chief secretion of the mouth is supplied by the sali- 
vary glands, which are three pairs of large compound saccular 
glands 1 called the parotid, submaxillary, and sublingual, respec- 
tively. Each parotid gland is placed just in front of the eai-, 
and its duct passes forwards along the cheek, until it opens 
into the interior of the mouth opposite the second upper molar. 
The submaxillary and sublingual glands are situated below 
the jaw and under the tongue, the submaxillary being placed 
further back than the sublingual. Their ducts open in the 
floor of the mouth beneath the tongue. The secretion of these 
salivary glands, mixed with that of the small glands of the 
mouth, is called saliva. 

The tongue. — The tongue is a freely movable muscular organ 
attached by its base to the hyoid bone. Besides being the 
special seat of the sense of taste, it is a useful aid in mastication 
and deglutition.2 

The teeth. — The semicircular borders of the upper and lower 
jaw-bones (the alveolar processes) contain thirty-two sockets for 
the reception of the teeth ; extending over the bones and a little 
way into each socket is a dense insensitive fibrous tissue covered 
by smooth mucous membrane, the gums. 

There are two sets of teeth developed during life : the first 
or milk teeth, and the second or permanent teeth. The cutting 
of the milk teeth begins usually at six months and ends with 
the second year ; there are only twenty of these teeth, and they 
are replaced during childhood by the permanent teeth .^ 

Each tooth consists of two portions, the crown and the fang : 
the crown projects into the cavity of the mouth, the fang is 
embedded in the socket. According to their shape and use the 
teeth are divided into incisors, canines, bicuspids, and molars. 

1 For description of compound glands see Section I. Chapter XIV. 

2 A detailed description of the tongue will be found in the chapter on the 
organs of special sense. 

8 The milk teeth are usually cut in the following order, the teeth appearing 
first in the lower jaw: central incisors, 7th month ; lateral incisors, 7th to 10th 
month ; front molars, 12th to 14th month ; canine, 14th to 20th month ; back 
molars, 18th to 36th month. ' 

Chap. XV.] 



Beginning in the middle line of each jaw and counting from 
before backwards, there are four incisors, two canines, four 
bicuspids, and six molars in the upper and in the lower jaw. 
The incisors have wide sharp edges, and are specially adapted 
for cutting the food ; the canines, or eye teeth, have a sharp 
pointed edge, are longer than the incisors, and are specially 
useful for tearing food asunder, 
or, as in dogs and other car- 
nivora, for holding prey. The 
bicuspids, or false grinders, are 
broader, with two points or cusps 
on each crown : these teeth have 
only one fang, the fang, however, 
being more or less completely 
divided into two. The molars, 
or true grinders, have broad 

crowns with small pointed pro- 
jections, which make them well 
fitted for crushing and bruising 
the food : they each have two or 
three fangs. The twelve molars 
do not replace the milk teeth, but 
are gradually added with the 
extension of the jaws, the last or 
hindermost molars not appearing 
until twenty-one years of age : 
they are often on this account 
called "wisdom teeth." 

The teeth are composed of 
three bone-like tissues, enamel, 
dentine, and cement; these sub- 
stances are all harder than bone, 
enamel beinsr the hardest tissue 
found in the body. In the inte- 
rior of each tooth is a cavity, the pulp-cavity, which is filled 
with a highly vascular and nervous tissue called the dental pulp. 
The teeth are developed from epithelium in much the same way 
as the hairs; for description of which see page 192. 

The pharynx. — The pharynx or throat cavity is a musculo- 
membranous bag, shaped somewhat like a cone, with its broad 

Fig. 113. — The Mouth, Nose, and 
Pharynx, with the Larynx and 
Commencement of Gullet, seen 
in Section, a, vertebral column ; 6, 
gullet; c, trachea; d, larynx; e, epi- 
glottis ; /, soft palate, between/ and e 
is the opening at back of cavity or 
fauces ; g, opening of Eustachian tube; 
h, nasal cavity; k, tongue; I, hard 
palate; m, sphenoid bone at base of 
skull ; n, roof of nasal cavity ; o, p, q, 
placed in nasal cavity. 


end turned upwards, and its constricted end downwards to end 
in the oesophagus. It is about four and a half inches (114 mm.) 
long, and lies behind the nose, mouth, and larynx. Above, it 
is connected with the base of the skull, and behind, with the 
cervical vertebrae ; in front and on each side are apertures 
which communicate with the nose, ears, mouth, and larynx. 

Of these apertures there are seven : two in front above, lead- 
ing into the back of the nose, the posterior nares ; two, one on 
either side above, leading into the Eustachian tubes which com- 
municate with the ears ; one midway in front, the fauces ; and 
two below, one opening into the larynx and the other into the 
oesophagus. The mucous membrane lining the pharynx is well 
supplied with glands, and at the back of the cavity there is a 
considerable mass of lymphoid tissue. The muscular tissue in 
the walls of the pharynx is of the striped variety, and when the 
act of swallowing is about to be performed the muscles draw 
the pharyngeal bag upwards and dilate it to receive the food ; 
they then relax, the bag sinks, and other muscles contracting 
upon the food, it is pressed downwards and onwards into the 

The oesophagus or gullet. — The oesophagus is a comparatively 
straight tube, about nine inches (228 mm.) long, extending from 
the pharynx, behind the trachea, and through the diaphragm, to 
its termination in the upper or cardiac end of the stomach. 
The muscular fibres in the walls of the oesophagus are arranged 
in an external longitudinal and in an internal circular layer. 
The mucous membrane is disposed in longitudinal folds which 
disappear upon distension of the tube. The mucous mem- 
brane in the mouth, pharynx, and oesophagus is covered for 
the most part by stratified epithelium. 

The stomach. — The stomach is the most dilated portion of 
the alimentary canal. It is curved upon itself, so that below it 
■ presents along, rounded outline, called the greater curvature, 
and above a constricted, concave outline, called the lesser 

It is placed transversely in the abdominal cavity, immediately 
beneath the diaphragm, the larger expanded end lying in con- 
tact with the spleen, and the smaller end under the liver. The 
stomach has necessarily two openings : the one leading into the 
oesophagus is usually termed the cardiac aperture ; the other, 

Chap. XV.] 



leading into the small intestine, the pyloric. The pyloric aper- 
ture is guarded by a kind of valve composed of circular mus- 
cular fibres, which form a constricted ring projecting into the 
pyloric opening. By this arrangement, the food is kept in the 
stomach until it is ready for intestinal digestion, when the cir- 
cular fibres relax and allow it to pass. 

When moderately distended, the stomach measures about 
four inches (102 mm.) vertically and twelve inches (305 mm.) 
from side to side. It has four coats. The outer serous coat is 
formed by a fold of the peritoneum. The fold is slung over 
the stomach, in much the same way as we sling a towel over a 

Fig. 114. — Vertical and Longitudinal Section of Stomach, Gall-bladder, 
AND Duodenum. 1, oesophagus; 2, cardiac orifice of stomach; 5, lesser curvature; 
6, greater curvature; 8, rugre in interior of stomach; 9, pyloric orifice; 10, 11, 
13, interior of duodenum, showing valvulffi conniventes; 12, duct conveying bile, and 
P, duct conveying pancreatic juice, into the duodenum; 14, gall-bladder; 15, com- 
mencement of jejunum. 

clothes-line, and covers it before and behind. The anterior and 
posterior folds unite at the lower border of the stomach and 
form an apron-like appendage, the omentum, which covers the 
whole of the intestines. The omentum often contains a large 
amount of fat. 

The muscular coat of the stomach consists of three layers of 
unstriped muscular tissue : an outer, formed of longitudinal 
fibres ; a middle, of circular ; and an inner, of less well-devel- 



[Chap. XV. 

oped, obliquely disposed fibres. The alternate contraction and 
relaxation of these fibres causes the food to be carried round 
and round the stomach, and at the same time, subjects it to 
considerable pressure. 

The mucous membrane is very soft and thick, the thickness 
being mainly due to the fact that it is densely j)acked with small 
tubular glands ; it is covered with columnar epithelium, and in 
its undistended condition is thrown into folds or rugai. The 
surface is honeycombed with tiny shallow 
pits, into which the ducts or mouths of the 
tubular glands open. The glands are of 
two kinds, one kind secretes mucus, and the 
other the special secretion of the stomach, 
the gastric juice. The stomach is supplied 
with nerves from the sympathetic system, 
and also with branches from the pneumo- 
gastric nerve, which comes from the cerebro- 
spinal system. 

The small intestine. — The small intestine 
fills the greater part of the front abdominal 
cavity. It is a convoluted tube about 
twenty feet (G.O metres) in length, and 
gradually diminishes in size from its com- 
mencement to where it joins the large 
intestine. The small intestine is divided 
by anatomists into three portions. The 
first ten or twelve inches (254 to 305 mm.) 
is called the duodenum ; the succeeding 
two-fifths, the jejunum ; and the rest, the 
ileum. The intestines are invested by a fold of the peritoneum 
in much the same way as the stomach. In this situation, the 
fold of the peritoneum is called the mesentery, and between 
its two layers are numerous blood-vessels, lymphatics, and 
lymphatic glands. 

The muscular coat of the small intestine has only two layers : 
an outer, thinner and longitudinal ; and an inner, thicker and 

The mucous coat is highly developed. In the first place it 
is largely increased by being arranged in permanent folds, the 
valvulte conniventes (^vide Fig. 114), which project transversely 

Fig. 115. — An Intes- 
tinal Villus. «, a, a, 
columnar epithelium ; 
6, b, capillary network; 
c, c, lymphoid tissue 
and muscle fibres; d, 
lacteal vessel. 

Chap. XV.] 



into the interior of the tube. The onward course of the food 
is delayed by being caught in the hollows formed hy these 
folds, and thus more thoroughly subjected to the action of the 
digestive juices : this arrangement also affords a larger surface 
for absorption. The valvulse conniventes are not found in the 
beginning of the duodenum, but begin to appear one or two 
inches from the pylorus ; about the middle of the jejunum they 
begin to decrease in size, and in the lower part of the ileum 
they almost entirely disappear. 

Again, the surface of the mucous membrane is increased by 
the linger-like projections which are so close set as to give a 

Fig. 116. — Sectiox through the Lymphoh) Tissue of a Solitary Glanb. 
(Cadiat.) a, centre of the gland, with the lymphoid tissue fallen away; b, epithe- 
lium of mucous memhrane ; c, c, villi, with epithelium partly broken away ; d, crypts, 
or glands, of Lieberkiihu. 

shaggy or velvety appearance to the membrane. These projec- 
tions or villi, as they are termed, extend throughout the whole 
length of the small intestine, and are especially provided for 
purposes of absorption. Each villus is a portion of the mucous 
membrane, and consists of an external layer of columnar cells 
attached to a basement membrane, and of a central mass of lym- 
phoid tissue. In the centre of each villus is the rootlet of a 
lacteal vessel, while under the basement membrane is a network 
of capillaries. The blood-vessels and lymphatics of the villi 
communicate with networks of both vessels in the sub-mucous 



[Chap. XV. 

coat below. Besides these projections formed for absorption, 
the mucous membrane is thickly studded with secretory glands ; 
the larger number of these, found all over the surface of the 
intestine, are called the glands or crypts of Lieberkiihn. These 
glands are supposed to secrete the intestinal juice, suceus en- 

Again, in the corium of the mucous coat the lymphoid tissue 
is collected into numerous solitary ghmds or follicles, and into 
groups of glands, the Peyer's patches, the functions of which 
are not yet clearly understood. 

The large intestine. — The large intestine is about five feet 
(1.5 metres) long, and from two and a 
half to one and a half inches (63 to 38 
mm.) wide; it extends from the ileum 
to the anus. It is divided into the 
Ctecum, with the vermiform appendix, 
the colon, and the rectum. 

The ccecum {ccecus, blind) is a large 
blind pouch at the commencement of 
the large intestine. The small intes- 
tine opens into the side wall of the 
large intestine about two and a half 
inches (63 mm.) above its — the large 
intestine's — commencement, the coecum 
forming a cul-de-sac below the opening. 

Fig. 117. — Cmcvm, show- * j.j_ i j j. xt. i i r j_i 

iNGiTs Appendix, Entrance Attached to the iower end 01 the csecum 

OF Ileum, and Ileo-c^cal ig a narrow, worm-likc tube about the 

Valve. 1, caecum; 2, com- . c ^ ^ ■^ t 

meiicement of colon; 3, en- size ot a lead pencil, the veriiiitorm 

trance of ileum into the large 
intestine; 4, ileo-cpecal valve; 

appendix. The Ccecum and appendix 
6, aperture of vermiform ap- lie just beneath the abdominal Avail in 

pendix; 7, vermiform appen. ^^^^ ^^-^^^^ -^-^^ ^^^^.^^^ ^^, .^^^ p^^^^ y^^^ 

The opening from the ileum into the large intestine is provided 
with two large projecting lips of mucous membrane which allow 
the passage of material into the large intestine, but effectually 
prevent the passage of material in the opposite direction. These 
mucous folds form what is known as the ileo-csecal valve. 

The colon may be subdivided into the ascending, transverse, 
and descending colon, and the sigmoid flexure. The ascending 
portion runs up on the right side of the abdomen until it reaches 
the liver, then bends abruptly to the left, and is continued 


straight across the abdomen as the transverse colon until, reach- 
ing the left side, it turns abruptly and passes downwards as the 
descending colon. Reaching the left iliac region on a level with 
the margin of the crest of the ileum, it makes a curve like the 
letter S, — hence its name of sigmoid flexure, — and finally ends 
in the rectum. The rectum is from six to eight inches (152 to 
203 mm.) long ; it passes obliquely from the left until it reaches 
the middle of the sacrum, then it follows the curve of the sacrum 
and the coccyx, and finally arches slightly backwards to its 
termination at the anus. The anal opening is guarded by two 
circular muscles called, respectively, the internal and external 

The large intestine has the usual four coats, except near its 
termination, where the serous is wanting. The muscular coat, 
along the Ctecum and colon, has a peculiar arrangement. The 
longitudinal fibres are gathered up in three thick bands, and 
these bands, being shorter than the rest of the tube, the walls are 
puckered between them. The mucous coat possesses no villi 
or valvules conniventes, but is usually thrown into effaceable 
folds, somewhat like those of the stomach. It contains nu- 
merous glands, resembling the crypts of Lieberkiihn found in 
the small intestine. 

Accessory organs of digestion. — The accessory organs of diges- 
tion are the teeth and salivary glands (which have already been 
sufficiently described), the pancreas, and the liver. 

The pancreas. — The pancreas is a compound, secreting gland, 
closely resembling the salivary glands in structure, except that 
the secreting cavities are saccular in the salivary glands, and 
more distinctly tubular in the pancreas. The cavities are 
grouped in small lobes or lobules, each lobule having its own 
duct. The lobules are joined together by connective tissue to 
form lobes, and the lobes, united in the same manner, form the 
gland. The small ducts open into one main duct, which, run- 
ning lengthwise through the gland, pierces the coats of the duo- 
denum and pours its contents into the interior of the intestine. 
The secretion formed in the pancreas is called the pancreatic juice. 

In shape, the pancreas somewhat resembles a dog's tongue. 
It is a flat, elongated organ, about six to eight inches (152 to 
203 mm.) in length, one and a half inches (38 mm.) in width, 
and from half an inch to an inch (12.7 to 25.4 mm.) thick. 



[Chap. XV. 

It lies beneath the greater curvature of the stomach and at the 
back of the abdominal cavity. 

The liver. — The liver is the largest gland in the body, weigh- 
ing ordinarily from fifty to sixty ounces (1-118 to 1701 grammes), 
and measuring ten to twelve inches (251 to 305 mm.) from side 
to side, six to seven (152 to 178 mm.) from above downwards, 
and three inches (76 mm.) from before backwards in its thick- 
est part. It is a dark reddish-brown organ, placed in the upper 
right and middle portion of the abdomen, and extending some- 
what into the left hypochondriac region. The upper convex 

Fig. 118. — Posterior View of Pancreas. 1, pancreas; 2, pancreatic duct; 6, 
opening of coninion duct, formed by union of pancreatic and clioledoclius ducts, into 
duodenum; A, pyloric end of stomach; B, duodenum; C, part of gall-bladder; JJ, 
cystic duct ; E, hepatic duct ; F, choledochus duct. 

surface fits closely into the under surface of the diaphragm. 
The under concave surface of the organ fits over the right kid- 
ney, the upper portion of the ascending colon, and the pyloric 
end of the stomach. The liver is unequally divided into two 
lobes, the right being much larger than the left. It is covered 
by a layer of peritoneum, and is also suspended and kept in 
position by ligamentous bands. 

The liver not only differs in size from the other secreting 
glands ; it also offers other striking peculiarities. First, it re- 
ceives its supply of blood from two different sources ; namely, 
arterial blood from the hypatic artery, and venous blood from 
the stomach, spleen, pancreas, and intestines, by means of the 

Chap. XV.] 



portal vein.i Secondly, the different parts of the secretory 
apparatus, the cells, blood-vessels, and ducts, instead of being 
arranged as elsewhere in distinct tubes or sacs, are closely 
united and massed togetlier. The secreting cells are collected 
into small polyhedral or many-sided masses, called hepatic 
lobules ; the blood-vessels form networks around and in the 
lobules ; while the ducts which carr}^ away the secretion (bile) 
begin Avithin the lobules in the form of tiny channels, running 
between the cells. 

Fig. 119. — Unde:i Sukface of Liver, i, right lobe; 2, left lobe; 3, 4, 5, smaller 
lobes; 9, inferior vena cava; 10, gall-bladder; 11, 11, transverse fissure, or "gate of 
the liver," containing bila duct, hepatic artery, and portal vein. 

The whole liver is invested in an envelope or capsule of con- 
nective tissue (Glisson's capsule), and the lobules are divided 
from one another by very delicate partitions of areolar tissue, 
each lobule being about the size of a pin's head and filled witli 
the special liver cells. 

The large portal vein and the small hej^atic artery enter the 
liver together on its under surface at what is called the " gate 
of the liver," the bile duct passing out at the same place. Tlie 
branches of these three vessels, enclosed by loose connective 
tissue, in which are lymphatics and nerves, accompany one 
another in their course through the organ. The smallest 
1 Cf. note on lungs, p. 131. 



[Chap. XV. 

branches penetrate between the lobules, and, surrounding and 
lying between each lobule, are known as the mterlohular 
branches. From the interlobular branches of the portal vein, 
thus surrounding the circumference of each lobule, run capillary- 
vessels, somewhat like the spokes of a wheel. These capillaries, 
converging towards the centre, merge into a veinlet, the intra- 
lobular vein, which running down the middle of the lobule, 
empties into a vein at its base. This vein, lying at the base of 
each lobule, is called the suhlohular vein, and empties its con- 
tents into the hepatic veins, by means of which the blood is 
conveyed from the back of the liver into the inferior vena cava. 

Fia. 120. — Diagrammatic Representation of Two Hepatic Lobules. The 
left hand lobule is represented with the intralobular vein cut across; in the right 
hand one the section takes the course of the intralobular vein, p, interlobular 
branches of the portal vein; /*, intralobular branches of the hepatic veins; s, sub- 
lobular vein ; c, capillaries of the lobules. The arrows indicate the direction of the 
course of the blood. The liver-cells are only represented in one part of each lobule. 

Thus each lobule is a mass of hepatic cells, pierced everywhere 
with a network of blood capillaries. 

The bile ducts commence between the hepatic cells in the 
form of fine canaliculi lying between the adjacent sides of two 
cells and forming a close network, the meshes of which corre- 
spond in size to the cells. At the circumference of the lobules, 
these fine canaliculi pass into the interlobular bile ducts which, 
running in connection with the blood-vessels, finally empty into 
the two bile ducts which leave the liver at the opening, spoken 
of above as the "gate of the liver." 

The cells of the liver manufacture bile from the blood, and 

Chap. XV.] 



discharge this into the minute bile canaliculi, whence it passes 
into the bile ducts to be conveyed into the small intestine. 
The cells, however, perform another important function, in that 
they change some of the substances brought to them in the 
blood from the digestive organs in such a manner as to render 
these substances suitable for the nutrition of the body ; but, at 

Fig. 121. — Lobule of Rabbit's Liver, Vessels and Bile Ducts Injected. 
a, central or intralobular vein; b, b, interlobular veins; c, interlobular bile duct. 

present, it will be sufficient to consider the secretion of bile as 
the only function of the liver. 

The bile is taken from the liver by a right and left duct, 
which soon unite to form the hepatic duct. The hepatic duct 
runs downwards and to the right for an inch and a half (38 mm.), 
and then joins at an acute angle the duct from the gall-bladder, 


termed the cystic duct. The hepatic and cyslic ducts tof^ether 
form the common bile duct (^ductus communis choledochus^, 
which runs downwards for about three inches (76 mm.) and 
enters the duodenum at the same opening as the pancreatic 

The gall-bladder {vide Fig. 119) is a pear-shaped sac, lodged 
in a depression on the under surface of the right lobe of the 
liver. It is lined by columnar epithelium, and its walls are 
formed of fibrous and muscular tissue. It is held in position 
by the peritoneum, and serves as a reservoir for the bile. Dur- 
ing digestion the bile is poured steadily into the intestine ; in 
the intervals it is stored in the gall-bladder. 

To recapitulate : the digestive apparatus may be said to con- 
sist of a tube and of important accessory organs placed in close 
connection and communication with it. For convenience of 
description, the tube may be divided into sections, each of which 
is furnished with mechanical and chemical appliances for reduc- 
ing the food into a soluble condition. First, the mouth cavity, 
which is provided with muscular cheeks and movable jaw, 
tongue, teeth, and the chemical solvent, saliva, secreted by the 
salivary glands ; secondly, the two passages, the pharynx and 
oesophagus, serving to convey the food into the next section, 
the stomach, which is furnished with muscular walls for crush- 
ing and churning the food, and with glands to secrete the acid 
digestive solvent, the gastric juice ; thirdly, the small intestine, 
supplied with bile and pancreatic juice, and with a highly 
specialized mucous membrane adapted to both digestive and 
absorptive purposes ; and lastly, the large intestine, having 
feeble digestive properties, but serving to absorb all the nutri- 
tious portion of the food still remaining, and to pass the residue 
onwards to be finally thrown out of the body in the form of 



Digestion. — Digestion is the process by means of which the 
food we take into our mouths is transformed into a condition 
of solution or emulsion suitable for absorption into the blood. 
This transformation is rapid or gradual according to the nature 
of the food-stuffs the digestive solvents are called upon to dis- 
solve. We all know practically, for instance, that it takes much 
longer to digest a piece of beefsteak than a cup of bouillon, and 
that when we wish to save the digestive powers as much as pos- 
sible we place a person upon "liquid diet." 

The digestion of the various food-stuffs depends entirely on 
the action of a class of substances known as enzymes or fer- 
ments. Although the exact composition and method of action 
of enzymes is not understood, it may be said that an enzyme is 
a substance a small amount of which, under certain conditions, 
can by its presence convert certain other substances into still 
other substances without itself being destroyed, or weakened 
in any way. Thus, a small amount of the enzyme, pepsin, can 
in an acid solution convert proteids into another class of sub- 
stances known as peptones, without diminution in the quantity 
or strength of the pepsin used. The enzymes are usually the 
products of living organisms, and are not found in inorganic 

Remembering that the three solid food-stuffs are proteids, 
fats, and carbohydrates, we will proceed to describe how each 
of these is transformed into a soluble condition in its course 
through the alimentary canal. 



Changes the food undergoes in the mouth ; mastication and deg- 
lutition. — When solid food is taken into the mouth it is cut 
and ground by the teeth, being pushed between them again and 
again by the muscular contractions of the cheeks and the move- 
ments of the tongue until the whole is thoroughly crushed and 
ground down. During this process of mastication the salivary 
glands are excited to very active secretion, the saliva is poured 
in large quantities into the mouth, and mixing with the food 
moistens it and reduces it to a soft pulpy condition. A certain 
amount of air caught in the bubbles of the saliva also becomes 
entangled in the food. 

The food thus softened and moistened is collected from every 
part of the mouth by the movements of the tongue, brought 
together upon its upper surface, and then pressed backwards 
through the fauces into the pharynx. The elevation of the 
soft palate prevents the entrance of food into the nasal cham- 
bers, while the epiglottis bars its entrance into the air passages, 
and it is guided safely and rapidly through the pharynx into the 
oesophagus. Here it passes beyond the control of the will ; it 
is grasped by the oesophageal muscles and by a continuous and 
rapid peristaltic action is carried onwards and downwards into 
the stomach. 

Saliva. — Mixed saliva (spittle) as it appears in the mouth 
is a glairy, frothy, cloudy fluid, the glairiness or ropiness being 
due to mucus; micro-organisms are also present in it to some 
extent, and other foreign matters derived from the food. 

Saliva is mainly water containing but little solid matter, its 
specific gravity varying from 1002 to 1006. It depends for its 
special action, as a digestive solvent, upon an enzyme or fer- 
ment which it contains called ptyalin. 

The action of saliva upon the food. — The chief function of 
saliva is to soften and moisten the food and to assist in masti- 
cation and deglutition. It has, however, a certain digestive 
action upon food-stuffs, especially starch. Upon the fats and 
proteids it has very little effect except to render them softer 
and better prepared for the action of the other digestive 

By the ptyalin-ferment present in saliva, starch, which is an 
insoluble substance, is changed into malt sugar or maltose, a 
highly soluble and absorbable product. This change is best 


effected at tlie temperature of the body, in a slightly alkaline 
solution, saliva that is distinctly acid hindering or arresting 
the process. Boiled starch is changed more rapidly and com- 
pletely than raw, but the food is never retained in the mouth 
long enough for the saliva to more than begin the transforma- 
tion of starchy matters. After leaving the mouth, further con- 
version of starch into sugar is arrested by the acid reaction of 
the gastric juice, and digestion of this class of food-stuffs is 
practically suspended until they again come in contact with 
the alkaline secretions in the upper part of the small intestine. 

During the processes of mastication, insalivation, and deglu- 
tition, the food is first reduced to a soft pulpy condition ; sec- 
ondly, any starch it may contain begins to be changed into 
sugar ; thirdly, it acquires a more or less alkaline reaction. 

Changes the food undergoes in the stomach. — The entrance of 
food into the stomach acts as a stimulant to the whole organ. 
The blood-vessels dilate, the glands pour out an abundant secre- 
tion upon the mucous lining, and the different layers of the 
muscular coat are excited to a continuous action. Delayed in 
the stomach by the contraction of the pyloric ring-muscle, the 
puljDy mass of food is carried round and round, and thoroughly 
mixed with the gastric juice until it is dissolved into a thick, 
grayish soup-like liquid, called chyme. The chyme thus formed 
is from time to time ejected through the pylorus, accompanied 
by morsels of solid, less well-digested matter. This ejection 
may occur within a few minutes after the entrance of food into 
the stomach, but does not usually begin until from one to two 
hours after, and lasts from four to five, at the end of which 
time the stomach is, after an ordinary meal, completely emptied. 

Gastric juice. — Gastric juice, secreted by the small, tubular 
glands ill llie mucous lining of the stomach, is a thin, colour- 
less, or pale yellow fluid, of an acid reaction. It contains few 
solids, and is dependent for its specific action upon two enzymes 
called pejysin and rennin. Pepsin is only properly active in an 
acid solution, and we therefore find that free hydrochloric acid 
in the proportion of 0.2 per cent is always present in normal 
gastric juice. 

Action of gastric juice upon the food. — The gastric juice has 
no action upon starch, and upon fats it has at most a limited 
action; that is, if adipose tissue be eaten, it will dissolve the 


envelopes of the fat-cell and set the fat free, but it has no 
power to emulsify them. The essential property of gastric 
juice is the power it has of decomposing proteid matters and 
of converting them into a soluble substance called peptone. 
Whatever the proteid may be, whether the albumin of eggs, 
the gluten of flour in bread, the myosin in flesh, the result is 
the same, pepsin, in conjunction with an acid at the temperature 
of the body, transforms them into peptones. 

Peptones readily dissolve in water, and pass with ease through 
animal membranes. They are probably absorbed, as soon as 
formed, by the blood-vessels in the walls of the stomach, though 
some pass in the chyme through the pylorus into the small 

Changes the food undergoes in the small intestine. — The chyme 
on entering the duodenum, after an ordinary meal, is a mixture 
of various matters. It contains some undigested proteids ; some 
undigested starch ; oils from fats eaten ; peptones formed in the 
stomach, but not yet absorbed ; salines and sugar which have 
also escaped complete absorption in the stomach ; all mixed with 
a good deal of water and the secretions of the alimentary canal. 
This acid mixture passing into the duodenum excites reflexly 
the secretory action of the pancreas, and stimulates the bile to 
flow from the gall-bladder ; the glands of Lieberkiihn also be- 
come active, and all these secretions proceed to further change 
the food-stuffs that have escaped digestion in the stomach. 

Bile. — Bile, secreted in the lobules of the liver and stored in 
the gall-bladder until needed, is a fluid of a bright golden red 
colour, with an alkaline reaction. The chief solid constituents 
of bile are cholesterin, the bile-salts, and the colouring-matters 
or pigments. 

Action of bile on food. — Upon proteids and starch, bile has 
little or no digestive action. On fats, it has a slight solvent 
action, and, in conjunction with pancreatic juice, has the power 
to emulsify them. When bile is prevented from flowing into the 
alimentary canal, the contents of the intestine undergo changes 
which do not otherwise take place, and which lead to the devel- 
opment of various products, especially of ill-smelling gases. 
Lastly, the passage of fats through membranes is assisted by 
wetting the membranes with bile or with a solution of bile- 
salts. It is known that oil will pass to a certain extent through 


a filter-paper, kept wet with a solution of bile-salts, whereas it 
will not pass, or passes with extreme difficulty, through one kept 
wet with distilled water. 

Pancreatic juice. — Healthy pancreatic juice is a clear, some- 
what viscid tiuid, with a very decided alkaline reaction. It is 
actively secreted by the pancreas during digestion and flows 
into the intestine in conjunction with the bile. The Germans 
call the pancreas the " abdominal salivary gland," though the 
pancreatic juice has a far more extensive action than the saliva. 

Among other important constituents the pancreatic juice con- 
tains an enzyme called trypsin, which, like pepsin, has the power 
to transform proteids into peptones ; trypsin, however, requires 
an alkaline medium to effect this transformation, while pepsin, 
as we have already seen, requires the medium to be acid. 

Action of pancreatic juice upon food. — On starch pancreatic 
juice acts with great energy, rapidly converting it into mal- 
tose. On proteids it practically exercises the same influence 
as the gastric juice, for by it proteids are changed into peptones. 
On fats it has a twofold action : it emulsifies them, and it splits 
them up into fatt}^ acids and glycerine. If we shake up olive 
oil with water, the two cannot be got to mix : as soon as the 
shaking ceases, the oil floats to the top ; but if we shake up 
olive oil with pancreatic juice, the oil remains evenly suspended 
in it. The reason of this is, that the oil has been minutely 
divided into tiny droplets, and each droplet surrounded by a 
delicate envelope supplied from the albumin in the pancreatic 
juice, so that they cannot fuse together to form the large drops, 
which would soon float to the top.^ Secondly, the fats that are 
not emulsified are broken up into glycerine and fatty acids. The 
glycerine is absorbed, and the fatty acids in the presence of an 
alkali form soaps which are soluble in water and capable of 
absorption. It is probable that the greater part of the fat is 
absorbed by the latter method. 

Thus pancreatic juice is remarkable for the power it has of 
acting on all the food-stuffs, — starch, fats, and proteids. 

Succus entericus, or intestinal juice. — Succus entericus is a 
clear, yellowish fluid, having a faintly alkaline reaction and 

1 The pancreatic juice, in thus emulsifying the fats, gives the white colour to 
the chyle, which is its most striking external characteristic, the innumerable 
tiny oil-drops reflecting all the light that falls on its surface. 


containing a certain quantity of mucus. It is said to have a 
solvent action upon all the food-stuffs, but at best its powers 
are slow and feeble, and we have no satisfactory reason for 
supposing that the actual digestion of food in the intestine is 
to any great extent aided by it. 

During the passage of the food through the small intestine 
the remaining proteids, starch, and fats are converted into pep- 
tones, sugar, and emulsified fats or soluble soaps, and these 
products as they are formed pass either into the lymphatics, 
or into the blood-vessels in the intestinal walls, so that the 
contents of the small intestine, by the time they reach the ileo- 
csecal valve, are largely deprived of their nutritious constitu- 
ents. So far as water is concerned, the secretion of water into 
the small intestine maintains such a relation to the absorption 
from it that the intestinal contents at the end of the ileum, 
though otherwise much changed, are about as fluid as in the 

Changes in the large intestine. — We have no very definite 
knowledge of the particular changes which take place in the 
large intestine. The contents are acid, although the secretions 
of the intestinal wall are alkaline, and certain acid fermenta- 
tions must therefore take place in them. These are probably 
due to the action of micro-organisms ; but however this may 
be, the chief work of the colon is absorption. 

By the abstraction of all the soluble constituents, and espe- 
cially by the withdrawal of water, the liquid contents become, 
as they approach the rectum, changed into a firm and solid 
mass of waste matters, ready for ejection from the body, and 
called feces. 

The feces. — The feces consist of the undigested and indigesti- 
ble substances of the food : among them are the elastic fibres of 
connective tissue ; the cellulose, which is the chief constituent 
of the envelopes encasing the cells of plants ; the indigestible 
mucin of mucus. These three materials, together with some 
water, some undigested food-stuffs, and some excretory sub- 
stances found in the various secretions poured into the aliment- 
ary canal, form the bulk of the material expelled from the body. 

To sum up the digestive processes : — 

The transformation of the food we take into our mouths into 
products capable of absorption is mainly a chemical process. 


The mechanical subdivision, bruising, and crushing of the food, 
accomplished by the teeth and the muscular contractions of the 
walls of the alimentary canal, is merely a process of preparation 
for the solvent action of the digestive juices. Of these juices 
there are five, each having a special action. 

(1) The saliva, containing the digestive enzyme ptyalin, 
transforms starch into sugar. 

(2) The gastric juice, containing the enzyme rennin, and 
pepsin (an enzyme acting in the presence of an acid), trans- 
forms proteids into peptones. 

(3) The pancreatic juice, containing trypsin (an enzyme 
acting in the presence of an alkali), transforms proteids into 
peptones, and, by virtue of other constituents, transforms 
starch into sugar, and emulsifies fats or turns them into solu- 
ble soaps. 

(4) Bile, containing cholesterin, bile-salts, and other matters, 
assists the pancreatic juice in saponification and emulsion of 
fats, promotes absorption of the same, and modifies putrefactive 
changes in the intestine. 

(5) Intestinal juice, containing mucus, transforms all food- 
stuffs in a feeble fashion not clearly demonstrated nor under- 

All material that these solvents fail to transform into a soluble 
and absorbable condition is gradually worked downwards by 
the peristaltic contractions of the alimentary canal, and finally 
leaves the body as waste and useless matter. 

Note. — For the sake of simplicity, we have considered digestion in a broad 
way as the conversion of practically non-diffusible proteids and starch into more 
diffusible peptones and higiily diffusible sugar, and as the emulsifying and split- 
ting up of fats. There is reason to believe that some of the sugar may be 
changed into lactic acid, or even into butyric or other acids, and that some of 
the proteids are carried beyond the peptone condition. But there is no doubt 
that the greater part of the proteid is absorbed as peptone, that carbohydrates 
are mainly absorbed as sugar, and that the greater part of the fat passes into 
the body as an emulsion. 

Absorption. — We have now to consider how the products of 
digestion find their way out of the alimentary canal into the 
tissues of the body ; for, properly speaking, though the food 
may be digested and ready for nutritive purposes, it is, until 
it passes through the walls of the alimentary canal, still practi- 
cally outside the body. 


There are two paths by means of which the products of diges- 
tion find their way into the blood : (1) by the capillaries in the 
walls of the stomach and intestines ; and (2) by the lymphatics 
in the walls of the small intestine (the lacteals). 

(1) The network of capillary blood-vessels is spread, as we 
have seen (page 168), immediately beneath the basement mem- 
brane of the mucous coat lining the interior of the alimentary 
canal, and matters in solution pass readily by diffusion or osmo- 
sis from the interior of the stomach and intestines into the 
blood-vessels in their walls. All the blood from the digestive 
organs is taken by the portal vein to the liver, and the products 
of digestion are modified by the action of the liver before they 
are returned to the general circulation by the hepatic veins. 
The hepatic veins pour their contents into the inferior vena 
cava, and the blood, enriched with the products of digestion, 
finally finds its way into the right side of the heart, whence it 
is taken to the lungs for purification before being sent to all 
parts of the body. 

During the passage of the blood through the liver the liver- 
cells not only take from it the material they need to form the 
bile; they also take from it material to form a starchy sub- 
stance, called glycogen. This glycogen, stored in the liver-cells, 
is gradually doled out, as it is needed, to the blood. It is not 
doled out, however, in the form of glycogen, which closely 
resembles starch, and is, therefore, insoluble, but in the form 
of sugar (dextrose or glucose). Thus the liver is a very com- 
plex organ whose cells elaborate bile and glycogen, and by 
some ferment-body, contained within themselves, convert the 
glycogen into glucose. J 

(2) Matters in solution can pass into the blood-vessels, but 
some other provision is necessary for the absorption of the 
emulsified fats. We find, accordingly, in the villi, which so 
closely cover the internal surface of the small intestine, little 
rootlets or beginnings of lymphatic vessels, which are set apart 
for the absorption of the fatty products of digestion. 

These lymphatic rootlets or lacteals, as they are generally 
called, occupy the centre of each villus. The emulsified fats 
pass, probably aided by the bile, into the bodies of the columnar 
cells on the surface of the villi, and from thence find their way 
into the interior of the villus, and finally into the beginning of 


the lacteal. The lacteals carry this fatty matter or chyle to 
the larger lymphatics in the mesentery, and these empty their 
contents into the thoracic duct which opens above into the great 
veins on the riglit side of the neck. 

Thus the food in solution after passing through the liver, 
and the emulsified food after passing through the lymphatics, 
find their way into the right side of the heart. It is not to be 
understood that matters in solution do not find their way into 
the lacteals, nor, on occasion, emulsified fats into the blood- 
vessels, but, broadly speaking, the food-products find their way 
into the blood in the manner above described. 

Final destination of food-stuffs. — It is impossible to say defi- 
nitely what becomes of the different food-principles after they 
have once entered the current of the blood. In general, it may 
be said that the carbohydrates are used for the production of 
heat and work, and that the fats may be stored in the body and 
used as fuel. The proteids do all that can be done by the fats 
and carbohydrates, and, in addition, form the basis of blood, 
muscles, and all the connective tissues. 

Still we cannot say that the carbohydrates perform a cer- 
tain work in the body and nothing else, or that the pro- 
teids and fats do. It is, however, generally understood that 
the proteids, fats, and carbohydrates each do an individual 
work of their own better than either of the others can do 
it. They are also necessary in due proportion to the nutri- 
tion of the body and work together as well as in their separate 

The body has always a store of material laid by for future 
use. If this were not the case, a person deprived of food 
would die immediately, as he does when deprived of oxygen. 
The great reserve forces of the body are stored in the form 
of adipose tissue and glycogen. The glycogen is given out 
during the intervals of eating to supply material for heat 
and energy; the adipose tissue is not so readily available, 
but may be called upon during prolonged deprivation from 
food. For a certain time the heat of the body may be main- 
tained and work done on these substances, although no food 
except water be taken. 

In conclusion we may say the food in the blood supplies the 
wants of the body in five different ways : — 


" 1. It is used to form all the tissues of the body. 

" 2. It is used to repair the waste of all the tissues. 

" 3. It is stored in the body for future use. 

" 4. It is consumed as fuel to maintain the constant tempera- 
ture which the body must always possess in a state of health. 

"5. It produces muscular and nervous energy." (Professor 
At water.) 



In the last four chapters we have seen that the blood is con- 
stantly supplied by means of the respiratory and digestive 
mechanisms, with all the chemical substances it requires to 
maintain the life, growth, and activity of the body. These sub- 
stances, entering the current of the blood, are carried to all the 
tissues, and are incessantly combining with the chemical sub- 
stances of which these tissues are composed. These combina- 
tions are not left to chance ; each tissue has a special affinity 
for the chemical substance in the blood which it requires for its 
own growth and special form of activity ; the secretory cell of 
the liver picks out substances from which it can manufacture 
bile and glycogen ; the muscle fibre assimilates those that will 
promote the changes upon which depends the power of con- 
tractility. We know that the proteid compounds contain the 
most essential elements for the formation of all kinds of tissue, 
and that phosphate of lime is a necessary ingredient in the 
hardening of bone, but we are utterly ignorant of how it comes 
about that each tissue element is enabled to select the particular 
material it needs and to reject that which it does not require. 

Our bodies are masses of changing atoms, some of which, if 
we may so express it, are on the " up grade," to construct the 
various tissues, and some are on the " down grade," to form the 
waste matters which are the final products of the tissues' activ- 
ity. These changes, which are incessantly going on while life 
lasts, are described under the general term of metabolism ; the 
constructive changes being spoken of as anabolic, and the de- 
structive as katabolic, changes. The final products then of 



the metabolism of the body will be certain waste matters, and 
we shall now proceed to describe the mechanism of the organs 
by means of which these wastes are removed from the body. 

Elimination. — In passing through the blood and tissues of the 
body, the proteids, fats, and carbohydrates are transformed into 
urea (or some closely allied product), carbon dioxide, and water, 
the nitrogen of the urea being furnished by the proteids alone. 
Many of the proteids contain sulphur and also have phosphorus 
attached to them in some combination, and some of the fats 
taken as food contain phosphorus ; these elements are converted 
by oxidation into phosphates and sulphates, and are excreted in 
that form in company with the other salts of the body. 

Broadly speaking, then, the waste products are urea, carbon 
dioxide, salts, and water. These leave the body by one or other 
of three main channels, the lungs, the skin, and the kidneys. 
Some part, it is true, leaves the body by the bowels, for, as we 
have seen, the feces contain, besides undigested portions of food, 
substances which have been secreted into the bowels, and are 
therefore waste products ; but the amount of these is very small 
and, except in diseased conditions, of no special importance. 

The waste matters discharged relatively by the lungs, skin, 
and kidneys may be stated as follows : — 

By the lungs • The greater part of the carbon dioxide. 

A considerable quantity of water. 
By the skin : A variable but, on the whole, large quantity of 


A little carbon dioxide. 

A small quantity of salts. 
By the kidneys : All, or nearly all, the urea and allied bodies. 

The greater portion of the salts. 

A large amount of water. 

A very small quantity of carbon dioxide. 

We have already studied the mechanism by means of which 
the lungs rid the blood of carbon dioxide and water, and it now 
remains for us to consider the mechanism of the skin and kid- 
neys. In the present chapter we shall devote ourselves to the 
consideration of the kidneys, which secrete the urine, and the 
other urinary organs, the ureters, bladder, and urethra, which 
collect the urine and conduct it to the outside of the body. 

Chap. XVII.] 



Position and General Description of the Urinary Organs. 

The kidneys. — The kidneys are two compound tubular secret- 
ing glands placed at the back of the abdominal cavity, one on 
each side of the lumbar vertebrae. They are bean-shaped, with 
the concave side turned towards the spine, and the convex side 
directed outwards. Each kidney is about four inches (102 mm.) 
long, two (51 mm.) broad, and one (25.4 mm.) thick, and ex- 
tends from the eleventh rib 
to nearly the crest of the 
ilium, the right being a lit- 
tle lower than the left in 
consequence of the large 
space occupied by the 
liver. They are covered 
by a tough envelope of 
fibrous tissue called the 
capsule of the kidney, and 
are usually embedded in 
a considerable quantity of 

The ureters. — The ure- 
ters are the excretory ducts 
of the kidneys. They arise 
in the middle of the con- 
cave side, or hilus, of each 
kidney, and proceed ob- 
liquely downwards and in- 
wards through the lumbar 
region of the abdomen into 
the pelvis, to open ob- 
liquely by two constricted 
orifices into the base of the 
bladder. Each ureter is of the diameter of a goose quill, from 
sixteen to eighteen inches (406 to 457 mm.) long, and consists 
of muscular tissue lined by mucous membrane. The muscular 
coat is arranged in two la3^ers, an outer circular and an inner 
longitudinal. Outside the muscular coat is a layer of fibrous 
connective tissue carrying the blood-vessels and nerves with 
which the tube is supplied. 

Fig. 122. — The Renal Organs viewed 
FROM Behind. R, right kidney; A, aorta; 
A?', right reual artery ; Vc, inferior vena cava ; 
Vr, right renal vein; U, right ureter; Vu, 
bladder; fJa, urethra. 


The bladder. — The bladder is the reservoir of the urine. It 
is situated in the pelvic cavity behind the pubes, and is held in 
position by ligaments. During infancy it is conical in shape 
and projects above the upper border of the pubes into the hypo- 
gastric region. In the adult, when quite empty, it is placed 
deeply in the pelvis ; when slightly distended, it has a round 
form ; but when greatly distended, it is ovoid in shape and 
rises to a considerable height in the abdominal cavity. (J-^ide 
Plate VII.) When moderately distended, it measures about 
five inches (127 mm.) in length, and three inches (76 mm.) 
across, and the ordinary amount of urine which it contains is 
about one pint (0.473 litre). The bladder consists of plain 
muscular tissue lined by a strong mucous membrane, and is 
covered partially by a serous coat derived from the peritoneum. 
The muscular coat has three layers, the principal fibres of which 
run longitudinally and circularly, the circular fibres being col- 
lected into a layer of some thickness around the constricted 
portion or neck, where the bladder becomes continuous with 
the urethra. These circular fibres around the neck form a 
sphincter muscle which is normally in a state of contraction, 
only relaxing at intervals, when the accumulation of urine 
within the bladder renders its expulsion necessary. 

The base of the bladder is directed downwards and back- 
wards, and in the female lies in contact with the front wall of the 
vagina and the lower part of the neck of the uterus. The neck 
of the bladder is directed obliquely downwards and forwards. 

The urethra. — The urethra is a narrow, membranous canal, 
about an inch and a half (38 mm.) in length in the female, and 
extending from the neck of the bladder to the external orifice 
or meatus urinarius. It is placed beneath the symphysis pubis, 
and is embedded in the anterior wall of the vagina. Its direc- 
tion is obliquely downwards and forwards, its course being 
slightly curved, the concavity directed forwards and upwards. 
It admits of considerable dilatation, its normal diameter, how- 
ever, being about a quarter of an inch (6,3 mm.). It is lined 
by a mucous coat, which is continuous, externally, with that of 
the vulva, and, internally, with that of the bladder. The exter- 
nal muscular coat is also continuous with that of the bladder, 
but between the mucous and muscular coats is a layer of thin, 
spongy tissue, containing a network of large veins. 

Chap. XVII.J 



The structure of the kidney. — The kidney is a secreting gland, 
constructed upon the general plan of a compound secreting 
gland, but possessing special features peculiar to itself. If we 
cut a kidney in two lengthwise, it is seen that the upper end of 
the ureter expands into a basin-like cavity, into which the solid 
portion of the kidney projects in conical-shaped masses. This 
dilated cavity of the ureter is called the pelvis or basin of the 
kidney, and this 
pelvis is irregu- 
larly subdivided 
into smaller, cup- 
like cavities, called 
calices, which re- 
ceive the pointed 
projections of the 
kidney substance. 

The substance of 
the kidney is read- 
ily seen by the 
naked eye to con- 
sist of two distinct 
parts : an outer, 
darker, and more 
solid portion, called 
the cortex (bark), 
and an inner, lighter 
striated portion, 
called the medulla 
(marrow), which is 
not a solid mass but 
more or less dis- 
tinctly divided into pyramidal-shaped sections. The pointed 
projections or papillce of the pyramids are received by the irregu- 
larly disposed cup-like cavities of the pelvis. The bulk of the 
kidney substance, both in the cortex and medulla, is composed 
of little tubes or tubules, closely packed together, having only 
just so much connective tissue as is sufficient to carry a large 
supply of blood-vessels and a certain number of lymphatics and 
nerves. The different appearance of cortex and medulla is due 
to the shape and arrangement of tubules and blood-vessels. 

Fig. 123. — Section through the Kidney show- 
ing THE Medullary and Cortical Portions, and 
THE Beginning of the Ureter, ct, cortex; M, me- 
dulla; py, papilla of pyramidal section projecting into 
one of the calices of pelvis; E.A, renal artery; R.V, 
renal vein ; U, ureter. 



Examined under the microscope, it is seen that the urinifer- 
ous tubules begin as little rounded dilatations, called capsules, 
in the cortex of the kidney. These capsules are joined to the 

tubules by a constricted 
neck, and the tubules, after 
running a very irregular 
course, open into straight 
collecting tubes, which 
pour their contents 
through their openings in 
the pointed ends or papil- 
Ige of the pyramids, into 
the pelvis of the kidney. 
<iVide Fig. 126.) 

The tubules are com- 
posed of basement mem- 
brane, lined throughout by 
epithelium cells. The cells 
vary in the different parts 
of a tubule, some being 
more especially adapted 
to secretory purposes than 

The blood-supply of the 
kidney. — For its size, the 
kidney is abundantly sup- 
plied with blood. The 
renal artery, coming di- 
rectly from the aorta, 
divides as it enters the 
hilus of the kidney into 
branches, which, slipping 
around the pelvis, pass 
inwards between the pyra- 
mids. On reaching the 
boundary line between the 
cortex and the medulla, the branches divide laterally to form 
more or less complete arches (the veins also divide in a similar 
manner to form venous arches). From the arterial arches ves- 
sels pass upwards through the cortex, giving off at intervals 

Fig. 124. — Vascular Supply of Kidney, 
(Cadiat.) a, part of arterial arch; b, arterial 
branch passing upwards through the cortex ; 
c, glomerulus; d, efferent vessel ; e, meshwork 
of capillaries ; /, straight arterial vessels of 
medulla ; ff, venous arch ; fi, straight veins of 

Chap. XVII.] 




tiny arteries, each of which enters the dilated commencement 
or capsule of a uriniferous tubule. These tiny arteries, enter- 
ing the capsule, are spoken of as afferent vessels. They push 
the thin walls of the capsule before them, break up into a knot 
of capillary vessels, called a glomerulus, and finally issue from 
the capsule as efferent vessels. These efferent vessels do not 
immediately join to form veins, but break up into a close mesh- 
work of capillaries around the tubules, before they unite to 
form the larger vessels and pour their contents into the veins 
forming the venous arches, between the cortex and medulla. 
In this way the cortex of the kidney is supplied with blood. 
The medulla also receives its blood-supply mainly from the 
arterial arches. The blood passes down- 
wards in straight vessels between the uri- 
niferous tubules, to be returned by more 
or less straight veins to the venous arches, 
whence it is conveyed by large branches 
into the renal vein, which leaves the kid- 
ney at the hilus and pours its contents 
into the inferior vena cava. 

The renal artery in passing into the 
kidney is accompanied by a network of 
nerves, called the renal plexus. They 
are chiefly vaso-motor nerves, and regu- 
late the contraction and relaxation of the 
renal blood-vessels. 

' Secretion of urine. — Urine is secreted 
from the blood in two ways. It is partly removed by a process 
of transudation or filtration, and partly by the secretory action 
of the cells lining the uriniferous tubules. 

(1) Into the dilated extremity or capsule of each tubule a 
small artery enters and pushing the wall of the capsule before 
it breaks up into a bunch of looped capillaries. The blood in 
the loop of capillaries or glomerulus is only separated from the 
interior of the tubule by the thin walls of the capillaries and 
the inverted wall of the capsule, which closely covers the 
glomerulus. The artery entering the capsule is larger than 
the issuing vessel, and, during its passage through the glo- 
merulus, the blood is subjected to considerable pressure. As a 
result of this, a transudation of the watery constituents of the 

Fig. 125. — Plan of 
THE Blood-vessels con- 
nected WITH THE Tu- 



blood, with some dissolved salts, takes place through the walls 
of the blood-vessels and of the capsule into the tubule. 

(2) After leaving the capsule, the efferent vessel communi- 
cates with other similar vessels which together form a mesh- 
work of capillaries closely surrounding the tubules, so that the 

blood is again brought into close 
communication with the interior 
of the tubules. The tubules are 
lined with secreting cells, and 
these cells appear to have the 
power of selecting from the blood 
the more solid waste matters 
(especially the urea) which fail 
to filter through the flat cells 
forming the wall of the capsule. 
Thus the elimination of urine 
is a double process, being par- 
tially accomplished by transuda- 
tion, and partially by the selective 
action of the secreting cells lining 
the tubules. 

Excretion of urine. — The uri- 
niferous tubules commence in a 
dilated extremity, the capsule, and, 
after a very devious course, ter- 
minate in the collecting tubules 
which open on the pointed projec- 
tions or papillae of the pyramids. 
The fluid they contain passes into 
Fig. 126. — Diagram of the the pelvis of the kidney, whence it 

Course of Two Ukixiferous Tu- • ^„ ..,• j „i +i,„ „4-„,„ -.^j.^ 

BULEs. M, Maipighiau capsule, or ^^ Carried along the ureters into 

dilated extremity ; c, convoluted por- the bladder, partly by pressure and 

tionoftube; //, loop, consisting of a •, n ^11,1 

descending and ascending limb; D, gravity, and partly by the peri- 
collecting tubui© staltic contractions of the muscular 
walls of the ureters. In the bladder the urine collects, its re- 
turn into the ureters being prevented by the oblique entrance 
of these tubes into the walls of the bladder. 

Micturition is normally caused by the accumulation of urine 
within the bladder. The accumulation stimulates the muscular 
walls to contract, the resistance of the sphincter at the neck of 


the bladder is overcome, and the urine is ejected through the 
urethra. Involuntary micturition may occur as a result of 
spinal injury involving tlie nerve centres which send nerves 
to the bladder. It may be due to a want of " tone " in the 
muscular walls, or it may result from some abnormal irritation. 

General characters of the urine. — Normal urine may be de- 
scribecl as a transparent watery fluid, of a pale yellow colour, 
acid reaction, specific gravity of 1020, and possessing an odour 
which can only be described as " characteristic " or " urinous." 
Each one of these characters is liable to some variation within 
the limits of health as well as in disease. 

The transparency of urine may be diminished in health by the 
presence of mucus, derived from the genito-urinary tract, or by 
the deposit of salts. In disease the urine may become clouded 
by the presence of pus. 

The colour of urine depends mainly upon the amount of water 
it contains ; also upon a diminution or increase of colouring 
matters. In the copious urine of hysteria the colour is very 
light, while in the diminished flow in fevers it is very high. 
Abnormal colouring matters are derived from food or medicine, 
or result from some diseased condition. 

The reaction of urine should always be tested from a collec- 
tion of urine passed during twenty-four hours as it is aifected 
by diet and exercise. To test the reaction of urine, litmus 
paper is used. Acid urine turns blue litmus paper red; alka- 
line urine turns red litmus paper blue. When the colour of 
the paper remains unchanged the urine is said to be neutral. 
The reaction of mixed urine is normally acid. 

The specific gravity depends upon the amount of solid waste 
matters present in the urine. In health, it may vary from 1015 
to 1025. When the solids are dissolved in a large amount of 
water, the specific gravity will naturally be lower than when, 
from a deficiency of water, the urine is more concentrated. It 
is notably heightened by the presence of sugar in the disease 
called Diabetes Mellitus. 

The composition of urine. — The chief constituents of normal 
urine are water, urea, uric acid, colouring matters, and salts. Of 
these constituents, urea is by far the most important, for it is 
the chief solid waste product of the body. To eliminate urea is 
the special work of the kidneys, and if for any reason they fail 


to execute their work, the accumulation of urea in the system 
leads to termination of life. Urea is the final product of all 
proteid substances, and consequently a diet rich in proteids 
will increase the amount of urea in the system. When the 
kidneys are disabled, it is customary for physicians to lighten 
their work as far as possible by regulating the diet. 

Of the salts, chloride of sodium occurs in the largest quan- 
tity ; it sometimes disappears temporarily from the urine wi:en, 
in certain inflammatory diseases, it is needed by the biood. 

The chief abnormal constituents that are liable to appear in 
the urine are albumin, giving rise to a condition calleci albu- 
minuria, and sugar, giving rise to glycosuria. The " ca>. ts," 
which are found in urine in the various forms of Bright's ilis- 
ease, are shed from the tubules in the shape of cylindrical 

The quantity of urine passed in twenty-four hours. — The normal 
quantity of urine passed in twenty-four hours is from forty to 
fifty ounces (1.18 to 1.48 litres), or about three pints (1.42 
litres). This will vary in health with the condition of the skin, 
and the amount of fluid taken into the body. The excretion of 
water by the kidneys is closely related to that excreted by the 
skin. When the body is exposed to cold, the blood-vessels in the 
skin are constricted, and the discharge of water in the form of 
sweat is checked ; at the same time the blood-vessels of the kid- 
neys are dilated, there is a full and rapid stream of blood through 
the glomeruli, and an increased flow of urine results. On the 
other hand, when the body is exposed to warmth, the cutaneous 
vessels are widely dilated, and the skin perspires freely, while 
the renal vessels being constricted, only a small and slow stream 
of blood trickles through the glomeruli, and the urine which is 
secreted is scanty. The effect on secretion, however, is more 
marked by the amount of fluid absorbed through the alimentary 
canal; an increased secretion of water always follows an ordi- 
nary meal, and when large quantities of water are drunk the 
amount of urine is correspondingly increased. 

The supra-renal capsules. — Lying immediately above each kid- 
ney are two small flattened bodies of a yellowish colour. They 
are usually classified with the ductless glands, as they have no 
excretory duct. Each organ is invested by a fibrous capsule 
which sends fibres into the sflandular substance : these fibres 

Chap. XVII.] 



form a framework for the soft, pulpy substance of the gland, 
and within the spaces of the framework are groups of cells. 

The supra-renal capsules are plentifully supplied with blood- 
vessels, nerves, and lymphatics, and they contain some striking 
colouring matters. In disease of these organs, the skin fre- 
quently becomes "bronzed," from an increase of pigment or 
colouring matter. Their special normal functions are unknown. 


Urine in 24 hours. 

1500 grammes. 

23,250 grains. 

in 1000 parts. 









The soUds consist of — 





Uric acid 


Hippuric acid 








Pigments and fats 




Sulphuric acid 




Phosphoric acid 
































Having described the mechanism by means of which the lungs 
rid the body of carbon dioxide and water, and of how the kid- 
neys relieve it of urea, salts, and water, it now remains for us to 
explain how the skin plays its part in elimination by yielding 
up water, and a certain amount of carbon dioxide and salts. 

The skin. — The skin is not, like the kidneys, set apart to per- 


Fig. 127. — Section of Epidermis. (Ranvier.) H, horny layer, consisting of 
s, superficial horny scales; sw, swollen-out horny cells; s.l. clear layer; M, Malpig- 
hian layer, consisting of s.fir. granular layer; p, many-sided or prickle cells: c, 
columnar cells. Nerve fibrils may be traced passing up between the epithelium cells 
of the Malpighian layer. 


Chap. XVIII.] THE SKIK 213 

form one special function. It is an important excretory organ, 
but it is also an absorbing organ ; it is likewise the principal 
seat of the sense of touch, and serves, too, as a protective cover- 
ing for the deeper tissues lying beneath it. 

The skin, like a mucous membrane, consists of two distinct 
layers ; an epithelial covering, and a connective tissue basis. 
The epithelium is a stratified epithelium and is called the epi- 
dermis, or scarf-skin; the connective tissue layer is called the 
derma, cutis vera (true skin), or corium. The epidermis is com- 
posed of layers of cells, the deeper of which are soft and pro- 
toplasmic, while the superficial layers are hard and horny. 
Between the two layers is a fairly distinct line of granular- 
looking cells, the granules in which have been thought to form 
the horny matter in the superficial cells. In the coloured races 
the single layer of elongated cells next the corium contains 
pigment granules. 

The growth of the epidermis takes place by the multiplication 
of the cells in the deeper or Malpighian layer. As these cells 
multiply by cell-division, they push upwards towards the surface 
those previously formed. In their upward progress they 
undergo a chemical transformation, and the soft protoplasmic 
cells become converted into the flat, horny scales which are 
constantly being rubbed off the surface of the skin. 

The thickness of the epidermis varies in different parts of the 
body, measuring in some places not more than 2X0^^ of an 
inch (0.106 mm.), and in others as much as ^jt\\ of an inch 
(1.06 ram.). It is thickest in the palms of the hands and on 
the soles of the feet where the skin is most exposed to friction 
and pressure, but it forms a protective covering over every 
part of the true skin, upon which it is closely moulded. 

No blood-vessels pass into the epidermis ; it, however, receives 
fine nerve-fibrils between the cells of the Malpighian layer. 

The cutis vera or true skin is a highly sensitive and vascular 
layer of connective tissue. It is, like the mucous membranes, 
attached to the parts beneath it by a layer of areolar tissue, 
here named "subcutaneous," which layer, with very few excep- 
tions, contains fat. The connection in some parts is loose and 
movable, as on the front of the neck ; in others, close and firm, 
as on the palmar surface of the hand and on the sole of the 



The cutis vera is often described as consisting of two layers, 
a superficial or papillary layer, and a deeper or reticular layer. 

The surface of the superficial or papillary layer is increased 
by protrusions in the form of small conical elevations, called 
papillpe, and whence this layer derives its name. Tliese papillae 
contain for the most part looped blood-vessels, but they also con- 
tain the terminations of medullated nerve-fibres in the shape of 
little bodies, called tactile corpuscles. 

The papillse seem chiefly to exist for the purpose of giving 
the skin its sense of touch, being always well developed where 

Fig. 128. — Section of Skin showing Two Papilla and Deeper Layers of 
Epidermis. (Biesiadecki.) a, vascular papilla, with capillary loop passing from 
subjacent vessel, c; b, nerve-papilla, containing tactile corpuscle, t; d, nerve passing 
up to tactile body ; /,/, section of spirally winding nerve-tibres. 

the sense of touch is exquisite. The papilla? containing tactile 
bodies are specially large and numerous on the palm of the 
hand and the tips of the fingers, and on the corresponding 
parts of the foot, while on the face and back they are small and 
irregularly scattered. 

The reticular layer of the corium is a continuation of the 
papillary layer, there being no real division between them, and 
is made up of bundles of white fibrous and elastic tissue which 
gradually blend below with the subcutaneous areolar tissue. It 
contains networks of blood-vessels, lymphatics, and nerves. 

Chap. XVIIL] 



The appendages of the skin are the nails, the hairs, the 
sebaceous glands, and the sweat-glands. They are all devel- 
oped as thickenings, or as down-growths, of the Malpighian 
layer of the epidermis. 

The nails. — The nails are composed of clear, horny cells of 
the epidermis, joined together so as to form a solid, continuous 
plate. Underneath each nail, the true skin is modified to form 
what is called the bed or matrix of the nail. This bed is very 
vascular, and is raised up into numerous papillae. At the 
hinder part of the bed of the nail the skin forms a deep fold, in 
which is lodged the root of the nail. 

The growth of the nail is accomplished 
by constant multiplication of the soft 
cells in the Malpighian layer at the root. 
These cells are transformed into dry hard 
scales which unite into a solid plate, and 
the nail, constantly receiving additions 
from below, slides forward over its bed and 
projects beyond the end of the finger. 
When a nail is thrown off by suppuration, 
or torn off by violence, a new one will grow 
in its place provided any of the cells of 
the Malpighian layer are left. 

The average rate of growth of the nails 
Fig. 129. — Piece of ig about qV of an inch (0.79 mm.) per week. 

Human Hair. (Highly mi i •" rr.ii- 

maguitied.) «, cuticle; The hairs.— Ihe hairs are growths of 
b, fibrous substauce; c, the epidermis, developed in little pits, the 

medulla. ^ • c ■^^■ ^ i-i 11 !• 

hair-ioliicles, which extend downwards into 
the deeper part of the true skin, or even into the subcu- 
taneous tissue. The hair grows from the bottom of the little 
pit or follicle, the part which lies within the follicle being 
known as the root. The substance of the hair is composed 
of coalesced horny cells, arranged in different layers, and we 
usually distinguish three parts in the stem or shaft of hairs. 
An outer layer of delicate, scale-like cells, the cuticle ; a middle, 
horny, thick, and coloured portion, formed of elongated cells, 
the fibrous substance ; and a central pith formed of angular cells, 
the medulla. 

The root of the hair is enlarged at the bottom of the follicle 
into a bulb or knob, and this bulb is composed of soft-growing 


cells fitting over a vascular papilla which projects into the 
bottom of the follicle. The hair grows from the bottom of 
the follicle by multiplication of the soft cells which cover the 
papilla, these cells becoming elongated to form the fibres of the 
fibrous portion, and otherwise modified to form the medulla and 
cuticle. New hairs are produced indefinitely, so long as the 
papillie and soft cells remain intact. 

The follicles containing the hairs are narrow pits formed by 
the involutions of the true skin and the epidermis. They slant 

obliquely upwards, so that the 
hairs they contain lie down on 
the surface of the body. Con- 
nected with each follicle are 
small muscles of plain muscular 
tissue which pass from the sur- 
face of the true skin, on the side 
to which the hair slopes, obliquely 

Fig. 130. — Section of the Skin downwards, tO be attached tO 

SHOWING THE HAIRS AND SEBACEOUS ^hc bottOm Of thc folHcle. WhcU 

Glands, o, the epidermis; o, corium; 

c, muscles, attached to hair-follicles aud these muscles COlltract, aS they 

to uuder surface of epidermis. ^^-^^ ^^^^^1^^, ^j^^ influence of cold 

or terror, the little hairs are pulled up straight, and stand " on 
end " ; the follicle also is dragged upwards so as to cause a 
prominence on the surface of the skin, whilst the cutis vera, 
from which the little muscle arises, is correspondingly depressed: 
in this way the roughened condition of the skin known as 
" goose-skin " is produced. Hairs grow on an average at the 
rate of half an inch (12.7 mm.) per month. They are found all 
over the body, except on the palms of the hands and the soles of 
the feet, and on the last joints of the fingers and toes. 

The sebaceous glands. — The sebaceous glands are small saccu- 
lar glands, the ducts of which open into the hair-follicles. They 
are lined with epithelium, and secrete a fatty, oily substance 
(sebum) which they discharge into the hair-follicles. Several 
sebaceous glands may open into the same follicle, and their size 
is not regulated by the length of the hair. Thus, some of the 
largest are found on the nostrils and other parts of the face, 
where they often become enlarged with pent-up secretion. The 
sebum lubricates the hairs and renders them glossy ; it also 
exudes, more or less, over the whole surface of the skin, and 



keeps it soft and flexible. An accumulation of this sebaceous 
matter upon the skin of the foetus furnishes the thick, cheesy, 
oily substance, called the vernix caseosa. 

The sudoriferous or sweat-glands. — All over the surface of the 
skin are minute openings or pores. These pores are the open- 
ings through which the sweat-glands pour their secretions upon 
the surface of the body. The sweat-glands are tubular glands 
with their blind ends coiled into little balls which are lodged 
in the true skin or subcutaneous tissue ; from the ball the tube 
is continued as the excretory duct of the gland up through 
the true skin and epidermis, and finally 0]3ens on the surface 
by a slightly widened orifice. Each tube is lined by a secreting 

epithelium continuous 
with the epidermis. The 
coiled end is closely in- 
vested by a meshwork of 
capillaries, and the blood 
in the capillaries is only 
separated from the cav- 
ity of the glandular tube 
by the thin membranes 
which form their respec- 
tive walls. The secre- 
tory apparatus in the 
skin is somewhat simi- 
lar to that which obtains 
in the kidney ; in the 
one case the blood- 
vessels are coiled up within the tube, while in the other the 
tube is coiled up within the meshwork of blood-vessels. 

The sweat-oflands are abundant over the whole skin, but 
they are most numerous on the palm of the hand and on the sole 
of the foot; in the groin, and especially in the axilla, they are 
larger than in other parts of the body. At a rough estimate, 
the whole skin probably possesses from two to two and a half 
millions of these glands, and their combined secreting power is 
therefore very great. 

Perspiration or sweat. — The sweat is a transparent colourless 
fluid, of a distinctly salt taste and with a strong, distinctive odour. 
When the secretion is scanty it has an acid reaction, but when 

Fig. 131. — Coiled End of a Sweat-Gland 
a, the coiled end; h, the duct; c, network of capil 
laries, inside which the sweat-inland lies. 


abundant it is alkaline. The chief normal constituents of sweat 
are water, salts, fatty acids, and, some authorities state, a slight 
amount of urea. In various forms of kidney disease urea may 
be present in considerable quantity, the skin supplementing to 
a certain extent the deficient work of the renal organs. 

Quantity of perspiration. — Under ordinary circumstances, the 
perspiration that we are continually throwing off evaporates 
from the surface of the body without our becoming sensible of 
it. This insensible perspiration, as it is called, usually amounts 
to about a pint (0.473 litre) in the course of twenty-four hours. 
The amount, however, varies to a very great extent — with the 
condition of the atmosphere ; the amount of exercise taken ; 
the quantity of fluid drunk ; the action of the kidneys. Varia- 
tions also occur under the influence of mental emotions, the 
action of drugs, or are induced by certain diseased conditions. 
When more sweat is poured upon the surface of the body than 
can be removed at once by evaporation, it appears on the skin 
in the form of scattered drops, and we then speak of it as sen- 
sible perspiration. 

Less important functions of the skin. — Besides being an impor- 
tant excretory organ, the skin is to a slight extent an absorbing 
organ. In the sound, healthy skin, it is doubtful whether 
matters in solution can be absorbed through the epidermic 
covering, but if the horny layers of the epidermis be removed 
by blistering, or in any other manner, substances in solution 
readily pass into the blood-vessels in the true skin. Oily sub- 
stances, especially when well rubbed in, are absorbed without 
removal of the epidermis. 

Oxygen in small amount is also taken in through the skin, 
but this gain to the body is balanced by the carbon dioxide 
which is thrown off. 

To sum up : the skin excretes a large amount of water and a 
small amount of carbon dioxide and salts ; it absorbs a small 
amount of oxygen and, under certain conditions, oily substances 
and watery solutions ; it is a protective organ and a tactile organ ; 
it su[)ports two appendages, viz. the hair and nails, and keeps 
itself flexible, and the hair glossy, by the secretion of sebum. 

There is still another function of the skin to be considered 
before closing this chapter, and that is the part it plays in regu- 
lating the temperature of the body. 


Bodily heat. — In order that the bodily functions may be prop- 
erly performed, it is necessary for the body to maintain a certain 
temperature. Just as plants are killed by the frost, or withered 
by the heat of the sun, so our tissues die if the bodily tempera- 
ture falls below, or rises above, a certain limit. Our bodies, 
however, differ from plants in that they generate and regu- 
late their own temperature, and possess the power of adapting 
themselves to extremes of external heat and cold, without 
necessarily suffering any vital injury. But, although the ex- 
ternal tempei'ature of the atmosphere may vary considerably 
without hurting us, the bodily temperature must be kept at 
an average standard of 98.6° F. (37° C.) if we are to remain in 
a state of health. Slight variations are compatible with health, 
the temperature being normally a trifle higher after eating or in 
the evening of the day, but any variation over a degree above or 
below 98.6° F. is indicative of danger. 

Production of heat. — Heat in the body is produced by the 
chemical changes that are constantly going on in the tissues. 
Wherever metabolic changes are taking place, there heat is set free. 
These changes take place more rapidly in some tissues than in 
others, and in the same tissues at different times. The muscles 
always manifest a far higher rate of activity than the connec- 
tive tissues, and consequently the former evolve a larger pro- 
portion of the bodily heat than the latter. We might liken the 
different tissues of the body to so many fireplaces stored with 
fuel, the fuel in some of the fireplaces being more easily ignited 
and burning more rapidly than in others. The muscles and the 
secreting glands, especially the liver, are supposed to be the 
main sources of heat, as they are the seats of a very active 

Loss of heat. — The heat thus continually produced is as con- 
tinually leaving the body by the skin and the lungs, and by the 
urine and feces. It has been calculated that in every 100 parts 
about : — 

88 per cent is lost by conduction and radiation from the surface of 
the skin and the evaporation of the perspiration. 
9 per cent is lost by warming the expired air and the evapora.tion 

of the Avater of respiration. 
3 per cent is lost by warming the urine and feces. 


Distribution of heat. — The blood, as we know, permeates all 
the tissues in a system of tubes or blood-vessels. Wherever 
oxidation takes place and heat is generated, the temperature of 
the blood circulating in these tissues is raised. Wherever, on 
the other hand, the blood-vessels are exposed to evaporation, 
as in the moist membranes in the lungs, or the more or less 
moist skin, the temperature of the blood is lowered. The gain 
and loss of heat balance one another with great nicety, and 
the blood, circulating rapidly, now through warmer, and again 
through cooler tubes, is kept at a uniform temperature of about 
100° F. (37.8° C). In this way the whole body is warmed in 
somewhat the same way as we warm a house, the warm blood 
in the blood-vessels heating the tissues, as the hot water in the 
hot- water pipes heats the rooms in steam-heated dwellings. 

Regulation of heat. — We have seen that active changes in 
the body produce heat. The action of the muscles is a source 
of heat, the activity of the glands during digestion, the active 
changes taking place in the tissues during inflammation or 
suppuration, or the changes caused by some specific micro- 
organism, and we may say that there are normal and abnormal 
sources of heat. 

Normally, production of heat is balanced by loss of heat, and 
the chief regulator of this gain and loss is undoubtedly the 
skin. This is well seen in the case of muscular exercise. 
Every muscular contraction gives rise to heat, and yet during 
severe muscular exercise the temperature of the body does not 
rise, or rises only to a trifling extent. This is accounted for 
by the fact that when the muscular exertion causes the blood 
to circulate more quickly than usual, the blood-vessels in the 
skin dilate, the sweat-glands at the same time are excited to 
pour out a more abundant secretion, and the heated blood pass- 
ing in larger quantities through the cutaneous vessels (which 
are kept well cooled by the evaporation of the perspiration) 
the general average temperature of the body is maintained. 

In pyrexia, or fever, rise of temperature is due to some cause 
which, while increasing the metabolism of the tissues, at the 
same time interferes with the process by means of which the 
body rids itself of superfluous heat. We all know how hot and 
dry the skin is liable to become in fevers ; how we try to restore 
its function and lower the temperature by baths, sponging, and 


packs ; liow we recognize tlie first signs of restored function — 
the moist, warm sweat in tlie palm of the hand — as a pretty 
sure sign tliat the fever is " broken." If a very higli tempera- 
ture persists for any length of time, the metabolism of the tis- 
sues goes on at such a rapid rate that the capital of the body 
is soon exhausted. Every organ works with feverish activity, 
the heart and lungs increase their action, the pulse and respira- 
tion become more and more hurried, and consequently more and 
more feeble, until finally, unless relief is obtained, the patient 
dies of exhaustion. 

In exposure to variations of external temperature the skin is 
also the chief agent in regulating the heat of the body. Expos- 
ure to cold stimulates the nerve fibres which bring about reflexly 
a constriction of the blood-vessels. As a result, less blood is sent 
to the surface to be cooled, and the average blood-temperature 
is maintained. On the other hand, exposure to warmth causes 
reflexly a dilatation of the cutaneous blood-vessels, and more 
blood is sent to the surface to be cooled. Briefly, when the 
external temperature is high, the cutaneous blood-vessels dilate, 
and the sweat is also usually poured out upon the surface of 
the skin ; when the external temperature is low, the cutaneous 
blood-vessels contract, and the skin usually remains dry. 

By clothing we can aid the functions of the skin and the 
maintenance of heat ; though, of course, clothes are not in them- 
selves sources of heat. The object of clothing is, in winter, to 
prevent conduction and radiation of heat from the skin, and, in 
summer, to promote it. Of the materials used for clothes, linen 
is a good conductor ; calico or muslin not quite so good, while 
wool, silk, and fur are all bad conductors. 

Subnormal temperature. — In some maladies the temperature 
falls distinctly below the normal. This is no doubt chiefly due 
to diminished metabolism. In cases of starvation, the fall of 
temperature is very marked, especially during the last days of 
life. The diminished activity of the tissues first affects the cen- 
tral nervous system ; the patient becomes languid and drowsy, 
and finally unconscious ; the heart beats more and more feebly, 
the breath comes more and more slowly, and the sleep of uncon- 
sciousness passes insensibly into the sleep of death. 



In the chapter on the Nervous System it was stated that the 
result of the stimulation of a neurone depends not upon any 
peculiarity of the neurone itself, but upon its anatomical rela- 
tions to other neurones. For exam23le, the neurones of which 
the optic nerve is composed are not essentially different from 
those which compose the trigeminal nerve, or from those which 
compose the facial nerve ; but, as we will proceed to show, the 
results and the methods of their stimulation differ according to 
their anatomical relationships : — 

1. The dendrones of the optic nerve terminate in the retinal 
epitlielium. This retinal epithelium is of such a nature that it 
responds only to the stimulation of light falling into the eye. 
The impulses thus aroused pass along the optic axones to the 
central nervous system, where they connect with the dendrones 
of other neurones situated in the cord, or in the brain, and 
cause on the one hand reflexes, and on the other voluntary 
movements accompanied by the phenomenon of consciousness. 

2. The dendrones of the trigeminal nerve, which supjily the 
skin of the face, terminate in various ways, so that some are 
stimulated only by heat, some by cold, some by pressure, and 
the impulses thus aroused pass to the central nervous sj^stem 
along axones which have connections similar to those of the 
optic nerve. 

3. The dendrones of the facial nerve lie within the central 
nervous system, and they are normally stimulated by impulses 
which pass to them from other neurones in the brain or spinal 
cord. These impulses they transmit along their axones which 
terminate in the muscles of the face, and which are thus, volun- 






tarily or reflexly, caused to contract. All peripheral nerve 
fibres may thus be classified by the way in which they termi- 
nate, or, what is the same thing, by their physiological function. 
The following is such a classification : — 

_ \ Voluntary (endintr in the voluntary musclesV 

Efferent k i / / ^ • ^ j j-i ^ j- 

I Involuntary (e.g. vaso-constrictor and vaso-dilator ; cardio- 

, , j accelerator and cardio-inhibitory, etc.). 

[^ Secretory (ending in gland cells). 

r Reflex sensory (unaccompanied by the phenomena of conscious- 
Special sensory (accompanied by conscious sensation), viz. : — 
Pressure. Pain. Hearing. 

Heat. Muscle-sense. Equilibrium. 

Cold. Taste. Vision. 

In the preceding chapters ^ attention has been called to 
different varieties of efferent nerves, and to the fact that any 
of these nerves might be stimulated reflexly through appropriate 
afferent {i.e. reflex sensory) nerves. We have now to consider 
those afferent fibres, the special sensory, which are concerned 
with the special senses, and in connection therewith to study 
the structures in which these nerves terminate, and which are 
called the organs of special sense. 

Touch or pressure. — The special organs of the sense of touch 
(Fig. 128) are distributed over the entire surface of the body, 
being more or less numerous in all parts of the true skin. 
Stimulation of these organs produces a sensation of touch, and 
we distinguish not only differences in the intensity of the stimu- 
lus, but also the locality in which the stimulus is applied. The 
sensations produced by the stimulation of the touch endings in 
different parts of the body resemble each other, but are not iden- 
tical. We have learned by experience to associate these differ- 
ences (which are called the "local signs ") with the locality in 
which the end organ stimulated is situated. Thus if the hand be 
stimulated we have three perceptions in consciousness : first, 
that we have been touched; secondly, we are conscious of the 
degree of pressure, i.e. of the intensity of the stimulus; and 
thirdly, we are aware of tlie fact that it is the hand which has 
been touched. 

1 Nerves to Voluntary Muscles, page 72 ; Vaso-constrictor Nerves, page 137 ; 
Vaso-dilator Nerves, page 137 ; Cardio-accelerator, page 110 ; Cardio-inhibitory 
Nerves, page 110 ; Secretory Nerves, page 166. 


The power of discriminating between different pressures, 
and also the power to localize impressions, varies in different 
regions of the body. 

A careful study of the skin shows that the organs of touch 
are separated from each other by an appreciable distance, so 
that we may speak of " pressure points or areas " which are sepa- 
rated from one another by points or areas which are insensitive 
to pressure. 

Temperature. — In addition to the end organs of the sense of 
touch, there are also structures in the skin which are only 
stimulated by changes in temperature. These structures are 
of two kinds: stimulation of one causing the feeling of cold; 
stimulation of the other, the feeling of heat. The distribution 
of the end organs of the sense of heat and cold is punctiform 
like the pressure sense, and we may therefore speak also of 
"heat and cold" points, each of these points having its own 
local sign. 

Pain. — The nerve endings of the sense of pain are very 
widely distributed throughout almost the whole body. 

Muscular sense. — The end organs of the muscular sense are 
situated in the tendons and between the fibres of the muscles. 
They convey to us the sense of the tension and pressure under 
which our muscles are placed, and from this we infer the position 
of the various parts of the body. Thus their function is to aid 
in coordinating muscular action, in preserving equilibrium, and 
in estimating weight or resistance. 

Common sensation. — Under this heading may be grouped a 
number of sensations often of a very indefinite character. They 
are the various obscure sensations proceeding from the viscera, 
which may give us the feeling of well-being or of the reverse. 
The sensations of hunger, of thirst, and possibly of fatigue 
belong to this class. 

The sense of taste. — The special organ of the sense of taste is 
the tongue, which is a movable muscular organ covered with 
mucous membrane. This mucous membrane closely resembles 
the skin in structure, except that the papillce it contains are 
more highly developed. The papilhe project as minute 
prominences and give the tongue its characteristic rough 

Some of the papilla) are simple and resemble those found in 



the skin; the remainder are compound,^ and are only found on 
the surface of the tongue. Of these compound papillse there 
are three varieties. The hirgest, the circumvallate papilloe, are 
about eight or ten in number, and form a V-shaped row near the 
root of the tongue, with its open angle turned toward the lips. 

Fig. 132. — The Upper Surface of the Tongue. 1, 2, circumvallate papillae; 
3, fungiform papillae ; i, filiform papillae ; 6, mucous glands. 

The next in size are the fungiform papilloe^^ found principally on 
the tip and sides of the tongue. The smallest and most numer- 
ous are the filiform papillce, found all over the tongue, excepting 

1 A compound papilla i.s one large one bearing several smaller ones on its surface. 

2 The fungiform papillae resemble fungi, having an expanded upper portion 
resting on a short, thick pedicle. The circumvallate papillae resemble the fungi- 
form, except that they are surrounded by a wall of smaller papillae. 


the root, and bearing on their free surface a form of ciliated 
epithelium. In some animals the hair-like processes on the fili- 
form papillcB are horny in structure, and their tongues are cor- 
respondingly roughened, so that they supplement the teeth in 
the bruising and crushing of food. In man these hair-like pro- 
cesses are exceedingly delicate, and seem to be specially con- 
nected with the sense of touch, which on the tip of the tongue 
is highly developed, and which serves to guide the tongue in its 
variable and complicated movements. 

In the circumvallate, some of the fungiform papillse, and 
scattered also over the mucous membrane of the tongue and 
soft palate, are little clusters of cells lying in cavities of the 
epithelium, called taste-buds. The bases of these cell-clusters, 
or taste-buds, are supplied with nerve-fibres. The nerve-fibres 
are derived from the glosso-pharyngeal and from the lingual or 
gustatory, a branch of the trigeminal. The former supplies 
the back of the tongue, and section of it destroys taste in that 
region ; the latter is distributed to the front of the tongue, and 
section of it, similarly, deprives the tip of the tongue of taste.^ 

We often confound taste with smell. Substances which have 
a strong odour, such as onions, are smelled as we hold them in 
our mouths; and if our sense of smell is temporarily suspended, 
as it sometimes is by a bad cold in the head, we may eat garlic 
and onions and not taste them. Hence the philosophy of hold- 
insf the nose when we wish to swallow a nauseous dose. 

The sense of smell. — The nose is the special organ of the 
sense of smell. It consists of two parts, — the external fea- 
ture, the nose, and the internal cavities, the nasal fosste. The 
external nose is composed of a triangular framework of bone 
and cartilage, covered by skin and lined by mucous membrane. 
On its under surface are two oval-shaped openings — the nos- 
trils — separated by a partition. The margins of the nostrils 
are provided with a number of stiff hairs which arrest the pas- 
sage of dust and other foreign substances carried in with the 
inspired air. 

The nasal fossae are two irregularly wedge-shaped cavities, 
separated from one another by a partition or septum, and com- 
municating with the air in front by the anterior nares or nostrils, 

1 The exact location of the cell-bodies, of which these nerve-fibres are the 
dendrones, is uncertain, as is also the way in which their axones enter the brain. 



while behind they open into the back of the pharynx by the 
two posterior nares. Fourteen bones enter into the formation 
of the nasal cavities : the floor 
is formed by the palate and 
part of the superior maxillary 
bones ; the roof is chiefly 
formed b}^ the perforated (crib- 
riform) plate of the ethmoid 
bone, and by the two small 
nasal bones ; and in the outer 
walls we find, in addition to 
processes from other bones, 
the three scroll-like turbinated 
bones. The turbinated bones, 
which are exceedingly light 

and spongy, project into the 

, .^. 1 T • 1 xi Fig. 133. — Vertical Longitudinal 

nasal cavities, and divide them section of Nasal Cavity. 1, olfactory 

into three incomplete passages nerve; w, branch of fifth nerve; h, hard 

from before backwards, — the 

superior, middle, and inferior meatus. The palate and superior 
maxillary bones separate the nasal and mouth cavities, and the 
cribriform plate of the ethmoid forms the partition between the 
cranial and nasal cavities. 

The mucous membrane (sometimes called the Schneiderian ^ 
membrane), which closely covers the nasal passages, is thickest 
and most vascular over the turbinated bones. In some nasal 
troubles it becomes much thickened and swollen, and occludes 
the nasal passages to such an extent as to compel us to breathe 
through the mouth. It contains numerous mucous glands which 
secrete mucus for the purpose of keeping the membrane moist, 
— a condition which is essential to perfection of the sense of 

The sense of smell is confined to the upper air passages of the 
nose. Here the mucous membrane is remarkable in that it 
contains nerve-cells. These cells have short, thick dendrones 
which terminate in a bunch of short, hair-like projections pro- 
truding beyond the surface of the mucous membrane, so that 

1 From Schneider, the first anatomist who showed that the secretions of the 
nose proceeded from the mucous membrane, and not, as was formerly supposed, 
from the brain. 


the neurones are stimulated directly, and not through the inter- 
vention of modified epithelial cells. The axones of these cells 
unite to form numerous bundles of fibres which pass upward 
through the cribriform plate of the ethmoid bone and terminate 
in the olfactory bulb of the brain. 

Odorous particles in the air, passing through the lower, wider 
air passages, pass by diffusion into the higher, narrower nasal 
chambers, and falling on the mucous membrane provided with 
olfactory nerve-endings, produce sensory impulses which, ascend- 
ing to the brain, give rise to the sensation of smell. 

If we wish to smell anything particularly well, we sniff the 
air up into the higher nasal chambers, and thus bring the odor- 
ous particles more closely into contact with the olfactory nerves. 

Each substance we smell causes its own particular sensation, 
and we are not only able to recognize a multitude of distinct 
odours, but also to distinguish individual odours in a mixed 
smell. The sensation takes some time to develop after the con- 
tact of the odorous stimulus, and may last a long time. When 
the stimulus is repeated, the sensation very soon dies out, the 
sensory terminal organs quickly becoming exhausted. Mental 
associations cluster more strongly round sensations of smell 
than round any other impressions we receive from without. A 
whiff of fresh-mown grass ! What associations will it not con- 
jure up for those happy mortals who spent their childish days 
in country lanes and fields. 

The ear. — The ear is the special organ of the sense of hear- 
ing, and is made up of three portions, — the external ear, the 
middle ear or tympanum, and the internal ear or labyrinth. 

The external ear consists of an expanded portion, named pinna 
or auricle, and the auditory canal or meatus. 

The auricle is composed of a thin plate of yellow fibro-car- 
tilage, covered with skin, and joined to the surrounding parts 
by ligaments and a few muscular fibres. It is very irregular 
in shape, and appears to be an unnecessary appendage to the 
organ of hearing, except that the central depression, the concha, 
serves to some extent to collect sound-waves, and to conduct 
them into the auditory canal. 

The auditory canal is a tubular passage, about an inch and a 
quarter (32 mm.) in length, leading from the concha to the 
drum-membrane. It is slightly curved upon itself, so as to 



be higher in the middle than at either end. It is lined by a 
prolongation of the skin, which in the outer half of the canal is 
very thick and not at all sensitive, and in the inner half is thin 
and highly sensitive. Near the orifice the skin is furnished 
with a few hairs, and further inwards, with modified sweat- 
glands, the ceruminous glands, which secrete a yellow, pasty 
substance, resembling wax. 

The middle ear or tympanum is a small, irregularly flattened 
cavity, situated in the petrous portion of the temporal bone, 
and lined with mucous membrane. It is separated from the 

Fig. 134. — Semi-diagrammatic Section through the Right Ear. M, concha; 

G, the external auditory canal ; T, tympanic, or drum-membrane ; P, tympanum, 
or middle ear; o, oval window; r, round window. Extending from T to o is seen. 
the chain of the tympanic bones ; i?, Eustachian tube ; T, i?, <S, bony labyrinth; V, 
vestibule; 2?, semicircular canal; iS, cochlea; 6, Z, i', membranous labyrinth in semi- 
circular canal and in vestibule. A, auditory nerve dividing into branches for vesti- 
bule, semicircular canal, and cochlea. 

external auditory canal by the drum membrane (pnemhrana 
tympani), and from the internal ear by a bony wall in which 
there are two small openings covered with membrane, — the 
oval window or fenestra ovalis, and the round window ov fenes- 
tra rotunda. The cavity of the middle ear is so small that 
probably five or six drops of water would completely fill it. 
It communicates below with the pharynx b}^ the small passage 
called the Eustachian tube, through which air enters the cavity 
and serves to keep the atmospheric pressure equal on each 
side of the drum-membrane. The middle ear also communi- 


cates above with a number of bony cavities in the mastoid por- 
tion of the temporal bone.^ The cavities, called mastoid cells, 
are lined with mucous membrane, which is continuous with that 
covering the cavity of the tympanum. 

Stretching across the tympanic cavity is a chain of tiny mov- 
able bones, three in number, and named from their shape the 
malleus or hammer, the incus or anvil, and the stapes or stirrup. 
The hammer is firmly attached to the drum-membrane, and the 
stirrup is fastened into the oval window (also covered by mem- 
brane) leading into the inner ear. The anvil is placed between 
the hammer and stirrup, and attached to both by delicate 
articulations. These little bones are set in motion with every 
movement of the drum-membrane. Vibrations of the mem- 
brane are communicated to the hammer, taken up by the anvil 
and transmitted to the stirrup, which is driven slightly forward, 
and sets in motion the membrane covering the oval opening 
leading into the internal ear. 

The internal ear or labyrinth receives the ultimate termina- 
tions of the auditory nerve, and is, therefore, the essential part 
of the organ of hearing. It consists of (1) a bony labyrinth, 
which is composed of a series of peculiarly shaped cavities, hol- 
lowed out of the petrous portion of the temporal bone, and 
named from their shape the vestibule, the semicircular canals, 
and cochlea (snail-shell). This bony labyrinth is lined by a 
serous membrane, which secretes a watery fluid called the peri- 
lymph ; and lying within tlie l)ony labyrinth and peri-lymph is 
(2) a membranous labyrinth, which is composed of a series of 
sacs or tubes, fitting more or less closely within the vestibule, 
semicircular canals and cochlea, the two former being concerned 
with the sense of equilibrium, the last with the sense of hear- 
ing. The membranous labyrinth is filled with a watery fluid 
called endo-lympli. In its walls terminate the dendrones of the 
auditory nerve. Before its termination, the auditory nerve 
divides into two branches, the cochlear supplying the cochlea, 
the vestibular supplying the vestibule and semicircular canals. 
The cells of origin of these two branches constitute two ganglia 
situated in the region of the labyrinth. Their dendrones are 
distributed to the epithelial lining of the membranous sac, while 

1 The mastoid portion of the temporal bone is that rounded mass of bone 
■which one readily distinguishes behind the auricle. 


the axones form the trunk of the auditory nerve and pass back 
to the meduUa oblongata. 

The sense of hearing. — The cochlea consists essentially of a 
spirally wound canal containing a long series of fibres stretched 
across it like strings. These fibres increase in length from the 
base of the cochlea upward, and in their action resemble the 
wires in a piano, for vibrations of the endo-lymph of a certain 
rate set up vibrations in the fibres of a certain length. 

All bodies which produce sound are in a state of vibration 
and communicate their vibrations to the air with which they 
are in contact, and thus the air is thrown into waves, just as a 
stick waved backwards and forwards in water throws the water 
into waves. 

When air-waves, set in motion by sonorous bodies, enter the 
external auditory canal, they set the drum-membrane vibrating, 
stretched membranes taking up vibrations from the air with 
great readiness. These vibrations are communicated to the 
chain of tiny bones stretching across the middle ear, and their 
oscillations cause the membrane leading into the internal ear to 
be alternately pushed in and drawn out, and vibrations are in 
this w^ay transmitted to the peri-lymph. Each vibration com- 
municated to the peri-lymph travels as a wave over the ves- 
tibule, semicircular canals, and cochlea, and is transmitted 
through the membranous walls to the endo-lymph. The vibra- 
tions of the endo-lymph stimulate the cochlear nerve endings, 
and nervous impulses are conveyed by the auditory nerve to 
those parts of the brain, stimulation of which gives rise to the 
sensation of sound. 

The effect produced by a sonorous vibration continues for a 
short time after the cessation of its cause. Usually the interval 
between two different impulses is sufficient to allow the first 
impression to disappear before the second is received, and the 
ear distinguishes them in succession. But if they follow each 
other at equal intervals, with a certain rapidity, they produce 
the impression of a continuous sound ; and this sound has a 
higher or lower pitch according to the rapidity of its vibra- 
tions. It has been discovered that sound-waves following each 
other with a rapidit}^ of less than sixteen times per second, are 
separately distinguishable ; but above that frequency they are 
mergfed into a continuous sensation. When the sound-waves 


recur at irregular intervals, the only characters perceptible in 
the sound are its intensity and quality. But if they succeed 
each other at regular intervals, the sound produced has a 
position in the musical scale as a high or low note. The more 
frequent the repetitions, the higher the note ; but a limit is at 
last reached, at which the ear fails to perceive the sound, and 
an excessively high note is therefore inaudible. Sonorous 
vibrations, perceptible to man as musical notes, range between 
sixteen per second for the lowest notes, and 38,000 for the 
highest. (Dalton.) 

The sense of equilibrium. — Among the various means (such as 
sight, touch, muscular sense), whereby we are enabled to main- 
tain our equilibrium, coordinate our movements, and become 
aware of our position in space, one of the most important is the 
action of the vestibule and semicircular canals. The vestibule 
consists practically of a sac, from the walls of which project 
sensory hairs, in relation at their bases with the dendrones of 
the vestibular nerve. Among these hairs rest several small 
calcareous bodies called otoliths. Each semicircular canal con- 
sists of a curved tube enlarged at one end (ampulla). In this 

ampulla are hairs around which the 
dendrones of the vestibular nerve 

The hairs in the ampullce are stimu- 
lated by the flowing of the endo- 
lymph, and the canals are so arranged 
(Fig. 135) that any movement of the 

Fig. 135. — Diagram show- head causes an increase in the pressure 

ING Relative Position OF THE n ■, -, , . 

Planes in which the Semi- of the eudo-lymph in One ampulla, 

CIRCULAR Canals lie. rl, ^^^^ ^ corresponding diminution in 

anterior vertical canal; P.V., the ampulla of the parallel canal on 

posterior vertical canal; //., ,i -j. • i rni it 

horizontal canal; a, ampulla of ^^^^ opposite Side. Thus a nodduig 

Rt. anterior vertical canal; a', of the head to the right WOUld cause a 

ampulla of Lt. posterior verti- „ pit ir jt-.i 

cai canal. now 01 cudo-lymph irom a to 6 m the 

right anterior vertical canal, but from 
h' to a' in the left posterior vertical canal. Hence the pressure 
upon the hairs is decreased in a, but increased in «'. Such 
stimulations of the sensory hairs are transmitted by the den- 
drones of the vestibular nerve, through the cell-bodies of the 
vestibular ganglion and the axones of the auditory nerve, to 


the brain, and it is the function of the semicircular canals 
to give us a knowledge of the position of the head when at 
rest. The intensity and direction of the pressure of the oto- 
liths upon the sensory hairs of the vestibule are also thought 
to give us a like knowledge ; namely, the position of the head 
when at rest. 

The sense of sight. — The eye is the special organ of the sense 
of sight, and consists of the eyeball, or eye proper, and of acces- 
sory protective appendages, such as the eyebrows, eyelids, lach- 
rymal glands, etc. 

The eyeball is contained in a bony cavity, the orbit, which is 
padded with fat and lined with a membranous capsule, — the 
capsule of Tenon. This capsule is a serous sac, one layer of 
which is attached to the posterior portion of the eyeball, while 
the other lines the orbital cavity : in this way the eyeball is 
isolated from surrounding structures, and free movement with- 
out friction is insured. The orbit is shaped like a four-sided 
pyramid ; the apex, directed backwards and inwards, is pierced 
by a large opening — the optic foramen — through which pass 
the nerves and blood-vessels distributed to the eyeball. The 
base of the orbit, directed outwards and forwards, forms a strong 
bony edge for protecting the eyeball from injury. 

The eyeball is spherical in shape, but its transverse diameter 
is less than the antero-posterior, so that it projects anteriorly, 
and looks as if a section of a smaller sphere had been engrafted 
on the front of it. 

The eyeball is composed of three coats or tunics, and contains 
three refracting media or humours. They are as follows : — 

Tunics. — 1. Sclerotic and cornea. 

2. Choroid, iris, and ciliary processes. 

3. Retina. 

Refracting media. — 1. Aqueous. 

2. Crystalline lens and capsule. 

3. Vitreous. 

The sclerotic (derived from the Greek word signifying hard) 
covers the posterior five-sixths of the eyeball. It is composed 
of a firm, unyielding, fibrous membrane, thicker behind than in 
front, and serves to protect the delicate structures contained 
within it. It is opaque, white and smooth externally, and 



behind is pierced by the optic nerve. Internally it is stained 
brown where it comes in contact with the choroid coat. The 
cornea (derived from Latin cornu, horn, and therefore also sig- 
nifying hard) covers the anterior sixth of the eyeball. It is 
directly continuous with the sclerotic coat, which, however, 
overlaps it slightly above and below, as a watch-crystal is over- 
lapped by the case into which it is fitted. The cornea, like the 
sclerotic, is composed of fibrous tissue, which is both firm and 
unyielding, but, unlike the sclerotic, it has no colour, and is 

Fig. 136. — The Left Eyeball in Horizontal Section from Before Back. 
1, sclerotic; 2, junction of sclerotic and cornea; 3, cornea; 4, 5, conjunctival mem- 
brane; 7, ciliary muscle ; 10, choroid ; 11, 13, ciliary processes ; 14, iris ; 15, retina; 
16, optic nerve ; 17, artery entering retina ; 18, fovea centralis ; 19, region where 
sensory part of retina ends ; 20, ''1, 28, are placed on the lens ; 28, suspensory liga- 
ment placed around lens; 29, vitreous humour; 30, aqueous humour in anterior 

perfectly transparent : it has been aptly termed the " window 
of the eye." Both the cornea and the anterior portion of the 
sclerotic are covered by reflections of the mucous membrane 
lining the eyelids. This is called the conjunctiva, and, kept 
well lubricated by the secretions of the eye, gives the eyeball 
its peculiar shining and glossy aspect. The sclerotic is supplied 
with very few blood-vessels, and the existence of nerves in it is 
doubtful ; while the cornea has no blood-vessels, but is well 
supplied with nerves. 


The choroid, or vascular coat of the eye, is a thin dark-brown 
membrane lining the inner surface of the sclerotic. It is com- 
posed of connective tissue, the cells of which are large and 
filled with pigment, and it contains a close network of blood- 
vessels. It extends to within a short distance of the cornea, 
and then is folded inwards and arranged in radiating folds, like 
a plaited ruffle, around the lens and just behind the edge of 
the cornea. The choroid coat, properly speaking, terminates 
anteriorly in the ciliary processes, arranged, as above stated, in 
a radiating circle round the lens ; but closely connected with 
the anterior margin of the choroid is the iris. 

The iris (^iris, rainbow) is a coloured, fibro-muscular curtain 
hanging in front of the lens and behind the cornea. It is 
attached to the choroid, with which it is practically continuous, 
and is also connected to the sclerotic and cornea at the point 
where they join one another. Except for this attachment, it 
hangs free in the interior of the eyeball. In the middle of the 
iris is a circular hole — the pupil — through which light is 
admitted into the eye-chamber. The iris, like the choroid, 
is composed of connective tissue containing a large number of 
pigment cells and numerous blood-vessels. It contains in 
addition two sets of plain muscular fibres. One set forms a flat 
band round the margin of the pupil, and is called the sphincter 
or contractor of the jjupil ; the other set consists of radiating 
fibres converging from the circumference to the centre, and is 
called the dilator of the pupil. The action of these muscle-fibres 
is affected by light. Under the influence of a bright light 
the pupil involuntarily contracts so that less light is admitted 
into the eye-chamber ; in a dim light the pupil involuntarily 
dilates to admit as much light as possible. The posterior surface 
of the iris is covered by a thick layer of pigment-cells designed 
to darken the curtain and prevent the entrance of light. The 
anterior surface of the iris is also covered with pigment cells, and 
it is chiefly these latter which cause the beautiful colours seen in 
the iris. The different colours of eyes, however, are mainly due 
to the amount, and not to the colour, of the pigment deposited. 

The retina, the innermost coat of the eyeball, is the most 
essential part of the organ of sight, since it is the only one 
directly sensitive to light. The sclerotic is the protective, the 
choroid the vascular or nutritive, and tlie retina is the visual or 



perceptive, layer of the eyeball. It forms a nearly transparent 
membrane situated between the inner surface of the choroid 
and the outer surface of the vitreous humour, and extending 
from the exit of the optic nerve to the commencement of the 
ciliary processes. The structure of the retina is interesting 
in that it consists not only of a sensory epithelium and a single 
group of neurones, but contains also a second series of neurones. 

A study of the development of 
the retina explains this remark- 
able fact, for it shows that the 
retina is in part really an out- 
lying portion of the brain. 

The accompan3dng figure shows 
the relation of the neurones and 
epithelial cells. Here it will be 
observed that it is the axones of 
the second series of neurones which 
collect together to form the optic 
nerve, and after penetrating the 
choroid and sclerotic coats, pass 
back to terminate in the brain 
(Fig. 137). 

The retina is usually described 
as consisting of eight layers and 
two limiting membranes ; of these 
layers, that called the layer of 
rods and cones is the most remark- 
able. It is composed of specialized 
epithelial cells which are directly 
concerned in producing the sensa- 

by their (lendrones impulses from the tion of light. Rays of light pro- 
rod and cone cells and transmitting d^ce nO effect Upon the Optic nerve 
them by their axones to No, the . , •, • . , • c •^ 

Without the intervention ot tlie 
rods and cones. This is proved 
by the fact that at the exit of 
the optic nerve there are no rods 
and cones, and this spot is quite blind, rays of light falling upon 
it producing no sensation. There is one point of the retina 
which is of great importance, and that is the macula lutea, or 
yellow spot. It is situated about ^V of an inch (2.12 mm.) 

Fig. 137. — Diagram showino 
Relations of the Neurones and 
Sensory Epithelium in the Ret- 
ina. E, epithelial layer of nucleated 
rod and cone cells, rods being direct- 
ed towards choroid coat of retina; 
Ni, neurones of first series receiving 

neurones of the second series. The 
axones of the neurones of the second 
series pass along the inner surface 
of the retina to the blind spot, where 
they unite to form the optic nerve. 


to the outer side of the exit of the optic nerve. In its 
centre is a tiny pit (^fovea centralis) which is the centre of 
direct vision ; that is, it is the part of the retina which is 
always turned towards the object looked at. From this point 
the sensitiveness of the retina grows less and less in all direc- 
tions. In the fovea centralis the rods and cones are exceedingly 
numerous, while the other retinal elements have been pushed 
aside, as it were, forming an elevated margin around the pit. 

Light may be described as consisting of vibrations in the 
ether which pervades space. These ethereal vibrations enter 
the eye through the cornea, pass in through the pupil and 
refracting media, and strike on the retina. They penetrate the 
transparent retina until they fall upon the rod and cone cells. 
In these there occur certain substances which are acted upon by 
the light (much as the film of a photographic plate is acted upon 
by the light). The chemical changes which these substances 
undergo stimulate the adjacent dendrones, and the impulse 
passes througli the cell-bodies and the axones to the second 
series of neurones, and then through their dendrones and cell- 
bodies to their axones. These last converge towards the blind 
spot, where they unite to form the optic nerve, which, passing 
from the eye to the brain, conducts the sensory impulses derived 
from the chemical changes occurring in the rods and cones to 
the visual centre, and the perception of light is produced. 

As in the case of the end organs of touch, each had its local 
sign (see page 223), so each rod and cone has its own particular 
local sign, but this local sign is not associated in our minds with 
the part of the retina stimulated, as we associate touch with a 
certain portion of the skin stimulated. In the case of the retina, 
the local sign is associated with the source of the light which 
acts as the stimulus. Thus when the upper part of the retina is 
stimulated, we know that the source of light, the object which 
we see, is below the line of direct vision ; and when the lower, 
the right, or the left-hand portion of the retina is stimulated, 
we know that the object lies above the line of direct vision, or 
to the left or right of it, as the case may be. 

The refracting media of the eye. — The interior of the eyeball 
is divided into two chambers by the crystalline lens and iris. 
The "anterior chamber," the portion in front of the iris, is filled 
with a colourless, transparent watery fluid, the aqueous humour. 


The " posterior chamber " is filled with a semi-fluid gelatinous 
substance, the vitreous humour or body, so called from its glassy 
and transparent apj^earance. Its refractive power, though 
slightly greater than that of the aqueous humour, does not 
differ much from that of water. It distends the greater part 
of the sclerotic, supports the retina, which lies upon its surface, 
and preserves the spheroidal shape of the eyeball. 

The crystalline lens is a transparent refractive body, with con- 
vex anterior and posterior surfaces, placed directly behind the 
pupil, where it is retained in position by the counterbalancing 
pressure of the aqueous humour and vitreous body, and by its 
own suspensory ligament. It is a fibrous body, composed of 
long riband-shaped cells and enclosed in an elastic capsule. Its 
refractive power is greater than that of the aqueous or vitreous 
humour, and it acts by virtue of its double-convex form as a 
converging lens, bringing parallel or diverging rays to a focus 
on the posterior surface of the retina. The function of the 
crystalline lens is to bring to a focus all the rays of light 
emanating from each separate point in the object seen, so that 
all the light from each point falls on and stimulates a corre- 
sponding point on the retina. For if the eye consisted only of 
a sensitive retina, impressions of light could be received, but the 
form of objects would not be distinguished. 

The action of the lens in thus focussing the rays of light at 
a particular point may be illustrated in the following manner : 
If a sheet of white paj)er be held at a short distance from a 
candle-flame, in a room with no other light, the whole of the 
jDaper will be moderately and uniformly illuminated by the 
diverging rays. But if a double-convex lens, Avith suitable cur- 
vatures, be interposed between the j^aper and the light, the 
outer portions of the paper will become darker, and its central 
portion brighter, because a portion of the rays are diverted 
from their original course and bent inward. By varying the 
distance of the lens from the paper, a point will at last be found 
where none of the light reaches the external parts of the sheet, 
but all of it is concentrated upon a single spot ; and at this spot 
will be seen a distinct image of the candle and its flame, i.e. 
each point of the flame is now represented by a single point on 
the paper ; and if for the paper we were to substitute the 
retina, each point would stimulate one, and only one, small area 
of the retina. 



Perception of the figure of external objects therefore depends 
on the action of the crystalline lens in converging all the i&js, 
emanating from a given point, to a focus on the retina. When 
the lens of the eye is too convex, and its refractive power 
excessive, the rays of light convei'ge too soon and cross one 
another before reaching the retina , consequent!}-, the image 
produced is not concentrated and distinct, but. dispersed more 
or less over the surface of the retina, is diffused and dim. On 
the other hand, if the lens 
is too flat, the rays do not 
converge soon enough, and 
the imacre is ag^ain diffused 
and indistinct. To remedy 
a too great convexity of the 
lens in the short-siglited or 
myopic eye, concave specta- 
cles are used to disperse the 
rays ; to remedy the flattened 
lens in the hypermetropic or 
long-sighted eye, we employ 
convex glasses to concen- 
trate and focus the rays 
more quickly. 

A normal eye is capable 

of distinct vision through- fig. 138. -Diagram illustrating Rays 

out an immense range. We of Light convebging in a Normal Eye, 

,, . .,,. » (A), A Myopic Eye, (B), and a Hyper- 

can see the stars milnons ot metropic Eye (C). 
miles away, and with the 

same eye, though not at the same time, we can see objects within 
a few inches of us. To be able to see objects millions of 
miles away and within a short range, the eye has to accom- 
modate or adjust itself to different distances. This ac- 
commodation is accomplished mainly by the lens changing its 
convexity. In accommodation for near objects, the lens becomes 
more convex and the pupil of the eye likewise contracts. This 
convexity is brought about by muscular effort,^ and is always 
more or less fatiguing. The accommodation for distant objects 
is a pa.ssive condition, the convexity of the lens being unaltered 

1 Connected with the lens are tiny muscles, — the ciliary muscles, — contraction 
of which alters the shape of the lens. 


and the pupil of the eye dilated, and it is on this account that 
the eye rests for an indefinite time upon remote objects without 

The eyeball is often compared to a photographer's camera. 
It is essentially a hollow spherical box filled with fluids, hav- 
ing its interior surface darkened by pigment, and containing a 
system of lenses by means of which images can be formed, and 
a screen upon which they can be received. In front is a cur- 
tain or diaphragm (the iris), with a variable central aperture 
(the pupil) to regulate the amount of light admitted. 

The colour of light is considered to be analogous to the pitch of 
sound. As the latter is determined by the number of vibrations 
of the atmosphere which strike the ear in a second, so the former 
depends on the number of the waves of ether which strike the 
retina in a second. The lowest note of an ordinary musical scale 
has, as we have already remarked, sixteen vibrations per second; 
the highest, 38,000 per second. The number of ether-waves 
which strike the retiua in a second to produce the sensation of 
red (which lies at the bottom, so to speak, of the colour-scale) 
is estimated at 474,439,680,000,000. The number required to 
cause the sensation of violet, which lies at the other extreme of 
our colour-perception, is estimated at 699,000,000,000,000 ! 

The muscles which move the eyeball are the four straight or 
recti and the two oblique. They have been sufficiently de- 
scribed on page 60. 

The appendages of the eye are the eyebrows, eyelids and 
lachrymal glands. 

The eyebrows are composed of two arched eminences of 
thickened skin, connected with three muscles, which by their 
action control to a limited extent the amount of light admitted 
into the eye. The eyebrows are furnished with numerous 
short, thick hairs, lying obliquely on the surface. 

The eyelids are two folds, projecting from above and below 
in front of the eye. They are covered externally by the skin 
and internally by a mucous membrane, the conjunctiva, which 
is reflected from them over the globe of the eye. They are 
composed for the most part of connective tissue, which is 
dense and fibrous under the conjunctiva, where it is known 
as the tarsus. 

Embedded in the tarsus is a row of elongated sebaceous glands 



(the Meibomian glands ^), the ducts of which open on the edge 
of the eyelid. The secretion of these glands is provided to 
prevent adhesion of the eyelids. 

Arranged in a double or triple row at the margin of the lids 
are the eyelashes ; those of the upper lid, more numerous and 
longer than the lower, curve upwards ; those of the lower lid 
curve downwards, so that they do not interlace in closing the 
lids. The upper lid is attached to a small muscle which is 
called the elevator of the upper lid ; and arranged as a sphincter 
around both lids is the orbicularis palpebrarum muscle, which 
closes the eyelids, and is the direct antagonist of the elevator of 
the upper lid. 

The slit between the edges of the lids is called the palpe- 
bral fissure. It is the size of this fissure which causes the 
appearance of large and small eyes, as the size of the 
eyeball itself varies but little. The outer angle of this fissure 
is called the external canthus ; the inner angle, the iyiternal 

The eyelids obviously serve for the protection of the eye ; 
movable shades which by their closure exclude light, par- 
ticles of dust, and other 
injurious substances. 

The lachrymal gland is 
a compound gland, closely 
resembling the salivary 
glands in structure. It 
secretes the tears, and is 
lodged in a depression at 
the outer angle of the 
orbit. It is about the size 
and shape of an almond. 
Its ducts run obliquely 
beneath the conjunctiva, 
and open by a series of 
minute orifices upon the 
upper surface of the eye. 

After passing over the surface of the eyeball, the tears are carried 
away through minute openings in the inner angle of the eye into 

1 By inverting the eyelids, these glands may be seen through the conjunctiva 
lying in parallel rows. 

Fig. 139. — The Lachrymal Apparatus. 


the lachrymal sac, which is the upper dilated portion of the 
nasal duct. 

The nasal duct is a membranous canal, about three-quarters 
of an inch (19 mm.) in length, which extends from the lach- 
rymal sac to the inferior meatus of the nose, into which it opens 
by a slightly expanded orifice. 

The tears consist of water containing a little salt and albu- 
min. They are ordinarily carried away as fast as formed, but 
under certain circumstances, as when the conjunctiva is irri- 
tated, or when painful emotions arise in the mind, the secretion 
of the lachrymal gland exceeds the drainage power of the nasal 
duct, and the fluid, accumulating between the lids, at length 
overflows, and runs down the cheeks. 



The internal female generative organs are the vagina, uterus, 
Fallopian tubes, and ovaries. 

The vagina. — The vagina is a distensible and curved musculo- 
membranous canal, extending from the vulva to the uterus. 
The posterior wall is about three and a half inches (89 mm.) 
long, while the anterior wall is only three inches (76 mm.). 
The front or anterior wall is united by connective tissue with 
the posterior walls of the bladder and urethra, the partition or 
septum between the bladder and vagina being called the vesico- 
vaginal, and that between the urethra and vagina, the urethro- 
vaginal, septum. And, if we divide the posterior wall of the 
vagina into five sections, we find that the middle three-fifths is 
connected with the rectum, the united walls of rectum and 
vagina forming the recto-vaginal septum ; ^ the lower fifth is 
separated from the rectum and is joined to the perineum ; ^ 
while the upper fifth extends up behind the neck of the uterus. 

The vagina is made up of three coats, an outer, fibrous ; 
middle, muscular ; and inner, mucous. The muscular coat in- 
creases during pregnancy, and the mucous coat is arranged in 
transverse folds or rugse, which allow of dilatation of the canal 
during labour and birth. 

The uterus. — The uterus is a thick-walled, hollow, pear- 
shaped organ, situated in the middle of the pelvic cavity. 
Its upper end is a little below the level of the superior strait 
of the pelvis (vide page 46); its lower end projects into the 
vagina. The bladder lies in front of it ; the rectum, behind ; 

1 Perforations of the vesico-vaginal and recto-vaginal partitions constitute 
vesico-vaginal and recto-vaginal fistulae. 

2 The perineum is a triangular section of tissue, made up of muscles strength- 
ened vfith very strong fascia, placed between the rectum and vagina, and forming 
the floor of the pelvis. 



the vagina, below; and the small intestine rests upon it 
above. Its length is roughly estimated to be about three 
inches (76 mm.); its greatest width, one and one-half inches 
(38 mm.); and its thickness, one inch (25.4 mm.). At the 
end of pregnancy it attains the length of a foot (305 mm.) 

Fig. 140. — Section of Female Pelvis, showing Relative Position of Viscera. 

or more, and measures about eight to ten inches (203 to 
254 mm.) transversely. 

The uterus is divided for purposes of description into three 
parts, the fundus, body, and neck. The fundus is the roinided 
portion projecting above a line drawn transversely through the 
upper part of the organ. The body is the portion extending 
from the rounded section, the fundus, to the constricted section, 
the neck. The neck or cervix extends from the body of the 
uterus into the vagina. 


Owing to the thickness of its walls, the cavity of the uterus 
is comparatively small. The cavity is triangular in shape (v)» 
and has three openings, one at each upper angle, communicating 
with the Fallopian tubes, and one, the os internum, or internal 
mouth, opening into the cavity of the cervix below. The cav- 
ity of the cervix, which is, of course, continuous with the 
cavity in the body, is constricted above, where it opens into 
the body by means of the os internum, and below, where it 
opens exteriorly by means of the os externum, ^ or external 
mouth. Between these two openings, the cavity of the cervix 
is somewhat enlarged. 

The walls of the uterus consist mainly of bundles of plain 
muscular tissue, arranged in layers which run circularly, longi- 
tudinally, spirally, and cross and interlace in every direction. 
A part of the external surface is covered by a portion of the 
peritoneum in the form of broad ligaments, and the inner sur- 
face is lined by a mucous membrane. This mucous membrane 
is continuous with that lining the vagina and Fallopian tubes. 
It is highly vascular, provided with numerous mucous glands, 
and is covered with ciliated epithelium. 

The uterus is abundantly supplied with blood-vessels, lym- 
phatics, and nerves. The blood reaches the uterus by means 
of the uterine arteries from the internal iliacs, and the ovarian 
arteries from the aorta. Where the neck joins the body of 
the uterus, the arteries from both sides are united by a branch 
vessel, called the circumflex artery. If this branch is cut dur- 
ing a surgical operation, or a tear of the neck during partu- 
rition extends so far as to sever it, the hemorrhage is very 
profuse. The arteries are remarkable for their tortuous course 
and frequent anastomoses. The veins are of large size and cor- 
respond in their behaviour to the arteries. 

During pregnancy all the tissues of the uterus become much 
enlarged, undergoing what is called a physiological hupertropliy. 
The uterus increases in weight from two or three ounces (57 to 
85 grammes) to two or three pounds (907 to 1360 grammes). 
After parturition, it goes back to nearly its former size. The 
tissues all go through a gradual shrinkage, or what is called a 
physiological atrop>hy. The enlarged muscles especially undergo 

1 The OS externum is bounded by two folds or lips of the mucous membrane, 
the anterior of which is thick, and the posterior narrow and long. 



[Chap. XX. 

fatty degeneration and absorption, called " involution," in con- 
tradistinction to "evolution " or development. This process of 
involution is not accomplished under six weeks, and sometimes 
requires longer. 

The uterus is not firmly attached or adherent to any j)art of 
the skeleton. It is, as it were, suspended in the pelvic cavity, 
and kept in position by ligaments. A full bladder pushes it 
backward ; a distended rectum, forward. It alters its position, 
by gravity, with change of posture. During gestation it rises 
into the abdominal cavity. 

The uterus has five pairs of ligaments attached to it, the 
chief of which are the broad and round ligaments. The broad 

"rtsffie pasted throii^^ 

Fig. 141. — The Uterus and its Appendages. Anterior View. 

ligaments are folds of peritoneum slung over the front and back 
of the uterus, and extending laterally to the walls of the pelvis. 
The anterior fold covers the front of the uterus as far as the 
middle of the cervix, when it turns up and is reflected over 
the back wall of the bladder. The posterior fold covers the 
back of the uterus, and extends far enough below to also 
cover the upper one-fiftli of the back wall of the vagina, when 
it turns up and is reflected over the anterior wall of the rectum. 
Thus the uterus, Avith, and between its two broad ligaments, 
forms a transverse partition in the pelvic cavity, the bladder, 
vagina, and urethra being in the front compartment, and the 
rectum in the back compartment. The round ligaments are 
two rounded fibro-muscular cords, situated between the folds 
of the broad ligament. They are about four and a half inches 
(114 mm.) long, and extend from the upper angle of the uterus 
forwards and outwards to be inserted into the vulva. 


Fallopian tubes. — The Fallopian ^ tubes or oviducts are pro- 
vided for the purpose of conveying the ova from the ovaries 
into the cavity of the uterus. They are two in number, one on 
each side, and pass from the upper angles of the uterus in a 
somewhat tortuous course between the folds and along the 
upper margin of the broad ligament, towards the sides of the 
pelvis. Each tube is about four inches (102 mm.) in length, 
and is described as consisting of three portions : (1) the isth- 
mus^ or inner constricted half ; (2) . the ampulla, or outer 
dilated portion, which curves over the ovary ; and (3) the 
wfiDidibidmn, or trumpet-shaped extremity, the margins of 
whicli are frayed out into a number of fringe-like processes 
called fimhrice. One of these fimbriae is attached to the ovary. 
The uterine opening of the Fallopian tube is minute, and will 
only admit a fine bristle ; the abdominal opening (ostium ab- 
dominale) is comparatively much larger. 

The Fallopian tube consists, like the uterus, of three coats : 
the external or serous coat, derived from the peritoneum ; the 
middle or muscular coat, having a layer of longitudinal and of 
circular fibres ; and the internal or mucous coat, continuous at 
the inner end with the mucous lining of the uterus, and at the 
distal end with the serous lining of the abdominal cavity. This 
is the only instance in the body in which a mucous and serous 
lining are continuous with one another. 

When the ovum is ready for entrance into the Fallopian tube, 
the fimbriae of the free end grasp the ovary, the tiny germ-cell 
is safely conducted into the trumpet-shaped extremity, and is 
thence carried along by the peristaltic motion of the oviduct 
into the uterus. This transmission of the cell is also assisted 
by the ciliated epithelium lining the tube, the motion of the 
cilia wafting it onwards. 

The ovaries. — The ovaries are two small almond-shaped 
bodies, situated one on each side of the uterus, between the 
anterior and posterior folds of the broad ligament, and below 
the Fallopian tubes. Each ovary is attached by its inner end 
to the uterus by a short ligament — the ligament of the ovary; 
and by its outer end to the Fallopian tube by one of the fringe- 
like processes of the fimbriated extremity. The ovaries each 
measure about one and a half inches (38 mm.) in length, three- 
1 Named after Fallopius, an Italian anatomist. 



[Chap. XX 

fourths of an inch (19.0 mm.) wide, and one-third of an inch 
(8.5 mm.) thick, and Aveigh from one to two drachms (1.8 to 
3.5 grammes). Their function is to produce, develop, and 

Fig. 142. — Section of an Ovary. Very highly magnified. (Waldeyer.) 
a, germ-epithelium; b, egg-tubes; c, c, small follicles; d, more advanced follicle; 
e, discus proligerus and ovum; /, second ovum in same follicle (this occurs but 
rarely); g, outer tunic of the fdllicle; h, inner tunic; ;', membrana granulosa; 
k, collapsed retrograded follicle ; I, I, blood-vessels ; y, involuted portion of the 
germ-epithelium of the surface ; z, place of the transition from peritoneal to ger- 
minal or ovarian epithelium. 

mature the ova, and to discharge them when fully formed 
from the ovary. 

The ovaries consist of a framework of connective and muscu- 
lar tissue, usually called the stroma or bed of the organ ; and 
of numerous vesicles or follicles of different sizes, called the 
Graafian follicles. 


The stroma contains many blood-vessels and lymphatics. The 
outer portion is more condensed than the interior, and the whole 
is covered by a peculiar layer of columnar epithelium-cells, 
called germinal epithelium. 

The Graafian follicles are cavities dotted about in the stroma 
in large numbers. The smaller ones lie near the surface. The 
larger are more deeply embedded, and only approach the sur- 
face when they are ready to discharge their contents. The 
follicles have each their own proper wall or tunic, derived from 
the connective tissue of the stroma, and each is lined by a layer 
or layers of granular epithelium-cells, and contains an ovum. 
The granular layer of cells, closely lining the cavity of the follicle, 
is termed the memhrana granulosa, but at one or other side it is 
heaped up into a mass of cells which j)rojects into the cavity of 
the follicle and envelops the ovum. This mass of cells which 
immediately surrounds the ovum is called the discus proligerus. 

As the follicle matures, fluid collects in the cavity, and, in- 
creasing in amount, the follicle gradually becomes larger and 
more tense. It now approaches the surface and begins to form 
a protuberance like a small boil upon the outside of the ovary. 
Finally the wall of the ovary and the wall of the follicle burst 
at the same point, and the fluid (liquor foUlculi^ containing the 
ovum, with the loose, irregular mass of cells, the discus pro- 
ligerus, clinging to it, is set free. At the moment of rupture, 
the ovum is received by the Fallopian tube and afterwards con- 
veyed to the uterus. After the follicle has discharged its con- 
tents, it has done its work, and it passes through a series of 
degenerative changes, and eventually disappears. Thus in the 
same ovary some of the follicles are mature, or approaching 
maturity ; others are undergoing development ; while others 
are retrograding and disappearing. 

The ova are formed from the germ-epithelium on the surface 
of the ovary, the cells of which become enlarged and dip down 
into the stroma in the form of little elongated masses. From 
these groups of cells the Graafian follicles and the ova are pro- 
duced. The ovum is a single cell about -^^ inch (0.203 mm.) 
in diameter. It has (1) a thick, surrounding envelope or 
membrane, called the vitelline membrane or zona pellucida ; 
(2) within the membrane or cell-wall is the protoplasm of 
the cell, filled with fatty and albuminous granules, and usually 


called the vitellus or yolk ; (3) imbedded in the vitellus or yolk 
is a transparent, sharply outlined nucleus, the germinal vesicle ; 
and (4) in the germinal vesicle is a small dark nucleolus, the 
germinative spot. 

It is impossible for us to trace the growth and development 
of a fecundated ovum. The subject is too complicated for us 
to attempt to describe it in a book of this kind, and we shall, 
therefore, content ourselves with briefly describing the first two 
or three steps. 

Soon after leaving the ovary, the germinal vesicle and ger- 
minal spot in a fecundated ovum disappear, and the protoplasm 
begins to divide inside the vitelline membrane into two halves, 
in each of which appears a nucleus. The halves divide into 
quarters, the quarters into eighths, and so the subdivision con- 
tinues until a great number of minute cells are produced, which 
soon arrange themselves, close to each other like bricks in a 
wall, upon the inner surface of the vitelline membrane. The 
cells thus in close contact with one another form a membrane, 
called the epiblast. Upon this membrane a second one soon 
appears, formed in the same way and lining its inner surface. 
This is called the hypoblast. Subsequently a third membrane, 
the mesoblast, is developed between the epi- and hypoblast, and 
from these three membranes all the tissues and complicated 
structures of the body are evolved. 

Upon the arrival of the ovum in the uterus, it is grafted 
upon the mucous membrane. It usually lodges upon the upper 
surface of the uterus, between two folds of the mucous lining, 
which soon grow up all around it, and, as it were, bury the germ 
in a circular grave. From the thickened mucous membrane 
lying between the ovum and the uterine wall, the placenta is 
ultimately formed for the nourishment of the embryo. 

The mammary glands. — The mammary gland is a compound 
gland, formed of branching ducts ending in secretory recesses. 
The whole organ is divided by connective tissue partitions into 
a number of lobes, each of which possesses its own excretory 
duct opening by a separate orifice upon the surface of the 
nipple, the gland being in fact not a single gland, but several 
glands bound together. Just before opening on to the nipple, 
each excretory duct is widened into a flask-shaped enlarge- 


The walls of the ducts and of the secreting recesses are 
formed of a basement membrane lined by epithelium-cells. 
During lactation the secreting cells become much enlarged, 
and fatty globules are formed within them. The fatty glob- 
ules appear to be set free by the breaking down of the inner 
part of the cell, the protoplasm becoming dissolved also, and 
forming the proteid substances of the milk. At the beginning 
of lactation the cells are imperfectly broken up, so that numerous 
cells containing comparatively large masses of fat (the colostrum 
corpuscles) appear in the secretion. 

Human milk has a specific gravity of from 1028 to 1034, and 
when quite fresh possesses a slightly alkaline reaction. Its 
average composition in every 100 parts is : — 

Proteids 2 

Fats 2.75 

Sugar 5 

Salts 0.25 

Water 90 




Abdu'cens. [From the Lat. ab, "from," and duco, to "lead."] A term ap- 
plied to the sixth pair of cranial nerves which supply the external recti 
(abductor), muscles of the eye. 

Acetab'ulum. [From the Lat. acetwn, " vinegar."] A name given to the 
cavity in the os innominatum, resembling in shape an old-fashioned 
vinegar vessel. 

Acro'mion. [From the Gr. akron, " summit," and dnos, the " shoulder."] 
The triangular-shaped process at the summit of the scapula. 

Ad'enoid. [From the Gr. aden, a "gland," and eidos, "form" or "resem- 
blance."] Pertaining to, resembling a gland. 

Ad'ipose. [From the Lat. adeps, " fat."] Fatty. 

Afferent. [From the Lat. ad, " to," and fero, to " bear," to " carry."] Bear- 
ing or carrying inioards, as from the periphery to the centre. 

Ag'minated. [From the Lat. agmen, a " multitude," a " group."] Arranged 
in clusters, grouped. 

Albu'min. [From the Lat. albus, " white."] Animal albumin is the chief 
solid ingredient in the tuhile of eggs. 

Albuminu'ria. [A combination of the words " albumin " and " urine."] 
Presence of albumin in the urine. 

Aliment'ary. [From the Lat. alimentum, " food."] Pertaining to aliment or 

Alimenta'tion. The act of receiving nourishment. 

Alve'olar. [From the Lat. alveolus, a " little hollow."] Pertaining to the 
alveoli, the cavities for the reception of the teeth. 

AmcE'ba. [From the Gr. ameibo, to "change."] A single-celled, proto- 
plasmic organism, which is constantly changing its form by protrusions 
and withdrawals of its substance. 

Amce'boid. Like an amoeba. 

Amphiarthro'sis. [From the Gr. ampJio, " both," and arthron, a " joint."] 
A mixed articulation ; one which allows slight motion. 

Anaboric. [From the Gr. anaballo, to "tnrow" or "build up."] Pertaining 
to anabolism, the process by means of which simpler elements are built 
up into more complex. 

Anasthe'sia. [From the Gr. a, an, " without," and aisthanomai, to " per- 
ceive," to " feel."] A condition of insensibility. 



Anastomo'sis. [From the Gr. ana, " by," " through," and stoma, a " mouth."] 
Comniunication of branches of vessels with one another. 

Aor'ta. [Gr. ao?-te from cero, to "raise up."] The great artery that rises up 
from the left ventricle of the heart. 

Aponeuro'sis. [From the Gr. apo, "from," and neuron, a "nerve."] A 
fibrous membranous expansion of a tendon ; the nerves and tendons 
were formerly thought to be identical structures, both appearing as 
white cords. 

Arach'noid. [From the Gr. arachne, a "spider," a " spider's web," and eidos, 
" form " or " resemblance."] Resembling a tveb. 

Are'olar. [From the Lat. areola, a " small space," dim. of area.'] A term 
applied to a connective tissue containing small spaces. 

Ar'tery. [From the Gr. aer, "air," and iereo, to "keep."] Literally, an 
air-keeper (it being formerly believed that the arteries contained air.) 
A tube which conveys blood from the heart to all parts of the body. 

Arthro'dia. [From the Gr. arthron, a " joint."] A movable joint. 

Artic'ular. Pertaining to an articulation or joint. 

Asphyx'ia. [From the Gr. a, " without," and spliyxis, the " pulse."] Liter- 
ally, without pulse. Condition caused by non-oxygenation of the 

At'rophy. [From the Gr. a, " without," and trophe, " nourishment."] Wast- 
ing of a part from lack of nutrition. 

Aud'itory. [From the Lat. audio, auditum, to "hear."] Pertaining to the 
sense or organ of hearing. 

Aur'icle. [From the dim. of Lat. auris, the "ear."] A little ear, a term 
applied to the ea?--shaped cavities of the heart. 

Auric' ulo-ventric'ular. Pertaining to the auricles and ventricles of the heart. 

Ax'one. The name now given to the prolonged processes of the neurone, or 
nerve-cell. The axis-cylinder of the nerve-fibre. 

Az'ygos. [From the Gr. a, " without," and zygos, a "yoke."] Without a 

Bi'ceps. [From the Lat. bis, " twice," and caput, the " head."] A term 

applied to muscles having a double origin or two heads. 
Bicus'pid. [From the Lat. bis, " twice," and cuspis, the " point of a spear."] 

Having two points. 
Brach'iaL [From the Lat. brachium, the " arm."] Belonging to the arm. 
Buc'caL [From the Lat. bucca, the "cheek."] Pertaining to the cheek; 

the mouth cavity formed chiefly by the cheeks. 
Bur' sal. [From the Gr. bursa, a " bag."] Pertaining to bursce, membranous 


Cae'cum. [From the Lat. ccecus, " blind."] The blind gut. 

Ca'lices, pi. of Ca'lyx. [From the Gr. Z.a/^x, a "cup."] Anatomists have 

given this name to small cup-Yike membranous canals, which surround' 

the papilla? of the kidney, and open into its pelvis. 
Canalic'ulus, pi. Canalic'uli. [Dim. of Lat. canalis, a "channel."] A small 

channel or vessel. 


Can'cellated. [From the Lat. cancelli, " lattice-work."] A term used to 

describe the spongy lattice-work texture of bone. 
Can'thus. [(ir. Kanthos, the " angle of the eye."] The angle formed by the 

junction of tlie eyelids, the internal being the greater, the external the 

lesser, canthus. 
Cap'illary. [From the Lat. capilhis, "hair."] A minutely fine vessel, resem- 
bling a hair in size. 
Car'bon. An elementary body, one of the principal elements of organized 

Carbon Di-ox'ide. COg. Carbonic acid. 

Car'dio-inhib'itory. [From the Lat. kardia, " heart," and inhibeo, to " re- 
strain."] An agent which restrains the heart's action. 
Carot'ids. [Perhaps from the Gr. karos, "stupor," because pressing on them 

produces stupor.] The great arteries conveying blood to the head. 
Ca'sein. [From the Lat. caseus, " clieese."] The albumin of milk; the 

curd separated from milk by the addition of rennet, constituting the 

basis of cheese. 
Caud'a Equi'na. [Lat.] "Horse-tail." A term applied to the termination 

of the spinal cord, which gives off a large number of nerves which, when 

unravelled, resemble a horse's tail. 
Cel'lulose. Basis of vegetable fibre. 
Cerebel'lum. [Dim. of Lat. cerebrum, the "brain."] The hinder and lower 

part of the brain ; the little brain. 
Cer'ebrum. [Lat. the "brain."] Chief portion of brain. 
Ceru'minous. [From the Lat. cerumen, "ear-wax."] A term applied to the 

glands secreting cerumen, ear-wax. 
Choles'terin. [From the Gr. xule, "bile," and stear, "fat."] A tasteless, 

inodorous, fatty substance found in the bile, blood, and nervous tissue. 
Chon'drin. [From the Gr. chondros, "cartilage."] A kind of gelatin 

ol)tained by boiling cartilaf/e. 
Chor'dae Tendin'eae. [Lat.] Tendinous cords. 

Cho'roid. [From the Gr. chorion, "skin," and eidos, "form" or "resem- 
blance."] A skin-like membrane : the second coat of the eye. 
Chyle. [From the Gr. t?//os, "juice."] Milky fluid of intestinal digestion. 
Chyme. [From the Gr. kymos, "juice."] Food that has undergone gastric 

but not intestinal digestion. (Both chyle and chyme signify literally 

liquid or juice.) 
Cica'trix. [Lat. a " scar."] The mark or scar left after the healing of a 

Cil'ia. [Lat. the "eyelashes."] Hair-like processes of certain cells. 
Cil'iary. Pertaining to the cilia. 
Cil'iated. Provided with cilia. 
Circumval'late. [From the Lat. circumvallo, " to surround with a wall."] 

Surrounded by a wall. 
Clav'icle. [From the dim. of Lat. clavis, a "key."] The collar-bone, so 

named from its shape. 
Coc'cyx. [Lat. the " cuckoo."] The lower curved bone of the spine, 

resembling a cuckoo's bill in shape. 


Coch'lea. [Lat. a " snail," a " snail-shell " ; hence, anything spiral.] A 

term applied to a cavity of the internal ear. 
Coe'liac. [From the Gr. koilos, " hollow."] Pertaining to the abdominal 

Co'lon. [Gr. kolon.'] That portion of the large intestine which extends 

from the caecum to the rectum. 
Colos'trum. First milk secreted after labour. 
Colum'nae Car'ne£B. [Lat.] "Fleshy columns"; muscular projections in the 

ventricles of the heart. 
Colum'nar. Formed in columns : having the form of a column. 
Com'missure. [From the Lat. con, "together," and milto, missum, to "put."] 

A joining or uniting together. Something which joins together. 
Con'cha. [Lat. a "shell."] A term applied to the hollow portion of the 

external ear. 
Con'dyloid. [From the Gr. kondylos, a "knob," or "knuckle," and eidoSy 

"likeness."] A term applied to joints and processes of bone having 

flattened knobs or heads. 
Conjuncti'va. [From the Lat. con, "together," and jungo,junctum, to " join."} 

A term applied to the delicate mucous membrane which lines both eye- 
lids and covers the external portion of the eyeball. 
Co'rium. [Lat. the "skin."] The deep layer of the skin ; the derma. 
Cor'nea. [Fi'om the Lat. cornu, a " horn."] The transparent anterior portion 

of the eyeball. 
Coro'nal. [From the Lat. corona, a " crown."] Pertaining to the crown. 
Cor'onary. [From the Lat. corona, a " crown."] A term applied to vessels, 

ligaments, and nerves which encircle parts like a crown, as the coronary 

arteries of the heart. 
Cor'pus Callo'sum. [Lat.] " Callous body," or substance. A name given to 

the hard substance uniting the cerebral hemispheres. 
Cor'puscle. [From the dim. of Lat. corpus, a " body."] A sinall body or 

Cor'tex. [Lat. " bark."] External layer of kidney : external layer of brain. 
Cos'tal. [From the Lat. costa, a " rib."] Pertaining to the ribs. 
Cra'nium. [Lat.] The skull. 
Crassamen'tum. [From the Lat. crassus, " thick."] The thick deposit of 

any fluid, particularly applied to a clot of blood. 
Crena'ted. [From the Lat. crena, a "notch."] Notched on the edge. 
Crib'riform. [From the Lat. cribrum, a " sieve," and /orma, "form."] Perfo- 
rated like a siei^e. 
Cru'ra Cer'ebri. [From the Lat. cms (pi. crura), a "leg."] Legs or pillars 

of the cerebrum. 
Cry'pt. [From the Gr. krypto, to "hide."] A secreting cavity: a folli.^le 

or glandular cavity. 
Cu'ticle. [From the dim. of Lat. cutis, the "skin."] A term applied to the 

upper or epidermal layer of the skin. 
Cu'tis Ve'ra. [Lat.] The true skin ; that underneath the epidermal layer. 
Cys'tic. [From the Gr. kystis, the "bladder."] Pertaining to a cyst, — a 

bladder or sac. 


Cy'toplasm. [From the Gr. kiitos, a " cell," and plasso, to " form."] The 
name given by Kolliker to the contents of a cell: same as proto- 

Decussa'tion. [From the Lat. decusso, decussatum, to "cross."] The crossing 
or running of one portion athwart another. 

Del'toid. Having a triangular shape ; resembling the Gi'eek letter A (delta). 

Den'drone. The name given to the branching processes of the neurone which 
begin to divide and subdivide as soon as they leave the nerve-cell. 

Dex'trin. A soluble substance obtained from starch. 

Dex'trose. CgHj^Og. A form of sugar found in honey, grapes, and other 

Diabe'tes Mel'litus. [From the Gr. dia, "through," baino, "to go," and meli, 
" honey."] Excessive flow of sugar-containing urine. 

Dial'ysis. [From the Gr. dialyo, to "dissolve."] Separation of liquids by 

Diapede'sis. [From the Gr. dia, "through," and pedad, to "leap," to "go."] 
Passing of the blood-corpuscles through vessel walls without rupture : 
sweating of blood. 

Di'aphragm. [From the Gr. diaphrasso, to " divide in the middle by a parti- 
tion."] The partition muscle diciding the cavity of the chest from that 
of the abdomen. 

Diarthro'sis. [From the Gr. dia, "through," as implying no impediment, 
and arthron, a " joint."] A freely movable articulation. 

Dias'tole. [From the Gr. diastello, to " dilate."] The dilation of the heart. 

Dip'loe. [From the Gr.diploo, to "double," to "fold."] The osseous tissue 
between the tables of the skull. 

Diox'ide. [From the Gr. dis, " twice," and " oxide."] A compound contain- 
ing two atoms of oxygen to one of base, or metal. 

Dis'cus Prolig'erous, or germ disk. A term applied to a mass of cell cling- 
ing to the ovum when it is set free from the ovary. 

Dis'tal. [From the Lat. dis, " apart," and sto, to " stand."] Away from the 

Dor' sal. [From the Lat. dorsum, the " back."] Pertaining to the back or 
posterior part of an organ. 

Duc'tus Arterio'sus. [Lat.] Arterial duct. 

Duc'tus Veno'sus. [Lat.] Venous duct. 

Duode'num. [From the Lat. rfuoc/e^u', "twelve each."] First part of small 
intestines, so called because about twelve fingers' breadth in length. 

Du'ra Ma'ter. [Lat.] The " hard mother," called dura because of its great 
resistance, and mater because it was formerly believed to give rise to 
every membrane of the body. The outer membrane of the brain and 
spinal cord. 

Dyspnoe'a. [From the Gr. dys, "difficult," and pneo, to "breathe."] Diffi- 
cult breathing. 

Efferent. [From the Lat. effero, to " carry out."] Bearing or carrying out- 
wards, as from the centre to the periphery. 


Elimina'tion. [From the Lat. e, " out of," and liyiien, liminis, a " threshold."] 
The act of expelling waste matters. Eliminate signifies, literally, to 
throw out of doors. 

Em'bryo. The ovum and product of conception up to the fourth mouth, 
when it becomes known as the foetus. 

Enarthro'sis. [From the Gr. en, "in," and arthron, a "joint."] An articu- 
lation in which the head of one bone is received into the cavity of 
another, and can be moved in all directions. 

Endocar'dium. [From the Gr. endon, " within," and kardia, " the heart."] 
The lining membrane of the heart. 

En'dolymph. [From the Gr. endon, "within," and Lat. lympha, "water."] 
The fluid in the membranous labyrinth of the ear. 

Endothe'lium. [From the Gr. endon, "within," and thele, the "nipple."] A 
term applied to single layers of flattened transparent cells applied to 
each other at their edges, and lining certain surfaces and cavities of the 
body. In contradistinction to ephithelium. 

En'siform. [From the Lat. ensis, a " sword," and forma, " form."] Shaped 
Like a sicord. 

En'zyme or Enzy'ma. [From the Gr. en, "in," and zume, "leaven."] A term 
applied to a class of ferments. 

Ep'iblast. [From the Gr. ejn, "upon," and blastos, a "germ," or "sprout."] 
The external or upper layer of the geiininal membrane. 

Epider'mis. [From the Gr. epi, "upon," and derma, the "skin."] The outer 
layer of the skin. 

Epiglot'tis. [From the Gr. epi, "upon," and glottis, tlie "glottis."] The 
cartilage at the root of the tongue which forms a lid or cover for the 
aperture of the larynx. 

Epithe'lial. [From the Gr. epi, "upon," and thele, the "nipple."] Pertain- 
ing to the epithelium, the cuticle covering the nipple, or any mucous 

Eth'moid. [From the Gr. ethmos, a "sieve," and eidos, "form," "resem- 
blance."] Sieve-like. A bone of the cranium, part of which is pierced 
by a number of holes. 

Eusta'chian Tube. A tube extending from behind the soft palate to the 
drum of the ear, first described by Eustachius. 

Fallo'pian. A term applied to tubes and ligaments first pointed out by the 

anatomist Fallopius. 
Fas'cia, pi. Fas'ciae. [I^at.] A bandage, — that which binds ; a membranous 

fibrous covering. 
Fau'ces. [Lat., pi. of faux, faucis, the " throat."] The cavity at the back of 

the mouth from which the larynx and pharynx proceed. 
Fem'oral. Pertaining to the femur. 
Fe'mur. [Lat.] The thigh. 
Fenes'tra. [Lat.] A window. 

Fibril'la, pi. Fibril'lge. [Dim. of Lat. f bra, a "fibre."] A little fibre. 
Fibrin'ogen. A proteid in blood plasma, main constituent of fibrin. 
Fib'ula. [Lat. a "clasp."] The long splinter bone of the leg. 


Fil'iform. [From the Lat. Jilum, a " thread," and forma, " form."] Thread- 

Fim'briae. [Lat. " threads," a " fringe."] A border or /nn^e. 

Fim'briated. Fringed. 

Fis'sion. [From the Lat. Jindo, Jissum, to "cleave."] A cleaving or breafe- 
ing up into two parts. 

Foe'tus. The child in utero from the fifth month of pregnancy till birth. 

Follicle. [From the dim. of Lat. follis, a " bag."] A little bag ; a smaQ 

Fontanelle'. [Fr.] A little fountain. A term applied to the membranous 
spaces between the cranial bones in the new-born infant, in which the 
pulsation of the blood in the cranial arteries was imagined to rise and 
fall like the water in a fountain. 

Fora'men. pi. Foram'ina. [Lat.] An opening, hole, or aperture. 

Foramen Mag'num. [Lat.] A large opening. 

Fora'men Ova'le. [Lat.] An oval opening. 

Fos'sa, pi. Fos'ssB. [From the hat. fodio, fossum, to "dig."] A depression 
or sinus; literally, a ditch. 

Fo'vea Centralis. [Lat.] Central depression. 

Fun'dus. [Lat.] The base or bottom of any organ which has an external 

Fun'giform. [From the Lat. fungus, a " mushroom," and forma, " form."] 
Having the shape of a mushroom. 

Funic'ulus. [Dim. of Lat. funis, a " rope."] A little cord, or bundle of 
aggregated fibres. 

Fu'siform. [From the Lat. /us«s, a "spindle," and /orma, "form."] Spin- 

Ganglia, pi. of Ganglion. [From the Gr. gagglion, a " knot."] A knot-VikQ 
arrangement of nervous matter in the course of a nerve. 

Gas'tric. [From the Gr. gaster, the "stomach."] Pertaining to the stomach. 

Gastrocne'mius. [From the Gr. gaster, the "belly," and kneme, the "leg."] 
The belly-shaped muscle of the leg. 

Genioglos'sus. [From the Gr. geneion, the " chin," and glossa, the " tongue."] 
A muscle connected with the chin and tongue. 

Ginglymus. [From the Gr. gigglymos, a "hinge."] A hinge-]omt. 

Gladi'olus. [Dim. of Lat. gladius, a "sword."] The middle piece of the 

Glair'y. [From the Lat. clarus, "clear"; Fr. clair-l Like the c^ear white 
part of an egg. 

Gle'noid. [From the Gr. glene, a "cavity," and eidos, "form," "resem- 
blance."] A name given to a shallow cavity. 

Glomer'ulus. [Dim. of Lat. glomus, a " clue of thread," or " ball."] A 
botanical term signifying a small, dense, roundish cluster : a terra 
applied to the fta^Mike tuft of vessels in capsules of the kidneys. 

Glos'so-pharynge'al. [From the Gr. glossa, the " tongue," and pharygx, the 
"pharynx."] Belonging to the tongue and pharynx. 

Glot'tis. [Gr. the " mouthpiece of a flute."] The aperture of the larynx. 


Glute'i, pi. of Glute'us. [From the Gr. gloutoi, the " buttocks."] The mus- 
cles forming the buttocks. 

Gly'cogen. Literally, producing glucose. Animal starch found in liver, 
which may be changed into glucose. 

Glyco'suria. [From the Gr. glukus, " sweet," and ouron, " urine."] A con- 
dition in which an abnormal amount of sugar is present in the 

Graafian Fol'licles, or Ves'icles. A term applied to the hollow bodies in 
tlie ovaries, containing the ova. 

Gramme. [From the Gr. gramma^ The unit of weight of the Metric 
System. It is equivalent to 15.43 grains Troy. 

Gus'tatory. [From the Lat. gusto, gustatuni, to " taste."] Belonging to the 
sense of taste. 

Haemoglo'bin. [From the Gr. haima, "blood," and Lat. globus, a "globe," 
or "globule."] A complex substance which forms the principal part of 
the blood-globules, or red corpuscles of the blood. 

Haemorrhoi'dal. [From the Gr. haima, "blood," and rheo, to "flow."] Per- 
taining to haemorrhoids, small tumours of the rectum, which frequently 

Haver'sian Canals. Canals in the bone, so called from their discoverer, Dr. 
Clopton Havers. 

Hepat'ic. [From the Gr. hepar, hepatos, the "liver."] Pertaining to the 

Hi'lum, sometimes written Hi'lus. [Lat.] A small fissure, notch, or depres- 
sion. A term applied to the concave part of the kidney. 

Homoge'neous. [From the Gr. homos, " the same," and genos, " kind."] Of 
the same kind or quality throughout ; uniform in natui'e, — the reverse 
of heterogeneous. 

Hu'merus. [Lat. tlie "shoulder."] The arm-bone which concurs in form- 
ing the shoulder. 

Hj^ aline. [From the Gr. hyalos, "glass."] Glass-\\ke, resembling glass in 

Hjr'drogen. An elementary gaseous substance, which in combination with 
oxygen produces water, II2O. 

Hy'oid. [From the Gr. letter v, and eidos, " form," " resemblance."] The 
bone at the root of the tongue, shaped like the Greek letter v. ' 

Hypermetro'pia. [From the Gr. hyper, " over," " beyond," metron, " measure," 
and dps, the " eye."] Far-sightedness. 

Hyper'trophy. [From the Gr. hyper, " over," and trophe, " nourishment."] 
Excessive growth ; thickening or enlargement of any part or organ. 

Hj^poblast. [From the Gr. hypo, " under," and blastos, a " sprout " or 
" germ."] The internal or wider layer of the germinal membrane. 

Hypochon'driac. [From the Gr. hyjw, " under," and chondros, a " carti- 
lage."] A term applied to the region of abdomen under the cai-tilages 
of the false ribs. 

Hypoglos'sal. [From the Gr. hypo, " under, " and glossa, the " tongue."] A 
name given to a nerve which terminates under the tongue. 


ireum. [From the Gr. eileo, to " twist."] The longest twisting portion of 

tlie small intestine. 
Il'iac. Pertaining to the ilium. 
irium, pi. Il'ia. [From the Gr. eileo, to " twist."] The upper part of the 

OS innominatum ; the haunch-bone ; perhaps so called because the crest 

of the bone turns or twists upon itself. 
Infundib'ula. [Lat. pi. of infundibulum, a "funnel."] FMnne^shaped canals. 
In'guinal. [From the Lat. inguen, inguinis, the " groin."] Pertaining to 

the groin. 
Inos'culate. [From the Lat. in, "into," and osculum, a "little mouth."] To 

unite, to open into each other. 
Insaliva'tion. The process of mixing the saliva with the food in the act of 

In'sulate. [From the Lat. insula, an " island."] To isolate or separate from 

Intercel'lular. Lying letween cells. 

Interlob'ular. That which lies between the lobules of any organ. 
Inter' stice. [From the Lat. inter, "between," and sto or sisto, to "stand."] 

The space which stands between things ; any space or interval between 

parts or organs. 
Intersti'tial. Pertaining to or containing interstices. 
Intralob'ular. That which lies within the lobules of any organ. 
I'ris. [Lat. the "rainbow."] The coloured membrane suspended behind 

the cornea of the eye. It receives its name from the variety of its 

Is'chium. [From the Gr. ischtio, to " support."] The lower portion of the 

OS innominatum; that upon which the body is supported in a sitting 


Jeju'num. [From the Lat. jejunus, "fasting," "empty."] The part of the 
small intestine comprised between the duodenum and ileum. It has 
been so called because it is almost always found empty after death. 

Ju'gular. [From the Lat. jugulum, the " throat."] Pertaining to the throat. 

Kataboric. [From the Gr. kataballo, to "throw down."] Pertaining to 
katabolism, the process by means of which the more complex elements 
are rendered more simple and less complex. The opposite of anabolism. 

Lach'rymal. [From the Lat. lachryma, a " tear."] Belonging to the tears. 

Lac'tation. [From the Lat. lac, lactis, "milk."] The period of giving 7nilk. 

Lac'teal. A term applied to the lymphatic vessels in the intestines which 
absorb the milk-like fluid, the chyle, from the intestines. 

Lac'tic Acid. An acid obtained from sour 7nilk. 

Lacu'na, pi. Lacu'nas. [Lat. a "cavity," an "opening."] A little hollow 

Lambdoi'dal. [From the Gr. letter A (Lambda), and eidos, "form," '^ resem- 
blance."] Resembling the Gr. letter A. 

Lamel'la, pi. Lamellae. [Lat.] A thin plate or layer. 

Lar'ynx. The upper part of the air passage, between the trachea and the 
base of the tongue. 


Latis'simus Dor'si. [Lat. superlative of latftx, "broad," "wide," and dorsum, 
the " back."] The tvidest muscle of the back. 

Lec'ithin. [From the Gr. lekitJios, the " yellow of egg."] A complex, fatty- 
substance found in the brain ; in the 7/olk of eggs. 

Leu'cocyte. [From the Gr. leukos, "white," and kytos, a "cell."] A term 
used to denote the white or pale corpuscles in the blood and lymph. 

Lig'ament. [From the Lat. ligo, liffatum, to "bind."] Anything that binds 
or unites. 

Lin'ea Alba. [Lat.] The ichite line formed by the crossing of the apo- 
neurotic fibres in the middle line of the abdomen. 

Lin'ea Ilio-pectine'a. [Lat.] A line forming the brim of the pelvis, so 
named from subjacent bone and muscle. 

Litre. [From the Gr. litra.'] The unit of the measure of capacity of the 
Metric System. It is equivalent to 33.81 fluid ounces, United States 
pharmacopeia, and 35.196 imperial fluid ounces, British pharmacopeia. 

Lob'ule. [From the dim. of Lat. lobus, a " lobe."] A small lobe. 

Lum'bar. [From the Lat. lumbus, the " loin."] Pertaining to the loins. 

Lymph. [From the Lat. li/mpha, " water."] A colourless fluid, resembling 
ivater in appearance. 

Lymphat'ic. Pertaining to lymph ; a vessel or tube containing lymph. 

Lymphoid. [From the Lat. lympha, " water," and Gr. eidos, " form," " re- 
semblance."] Having resemblance to lymph. 

Mac'ula Lute'a. [Lat.] Yellow spot. 

Ma'lar. [From the Lat. mala, the "cheek."] Pei'taining to the cheek. 

Malle'olus, pi. Malle'oli. [Dim. of Lat. malleus, a "hammer."] A name 
given to the pointed iirojections formed by the bones of the leg at the 

Malpig'hian Bod'ies. [So called in honor of Malpighi, a celebrated Italian 
anatomist.] A term applied to small bodies or corpuscles found in the 
kidney and spleen. 

Manu'brium. [Lat. a "haft," a "handle."] Name given to the upper por- 
tion of the breast bone. 

Mar'garin. One of the three chief constituents of fat. 

Mas'seter. [From the Gr. massaomai, to " chew."] One of the muscles of 

Mas'toid. [From the Gr. maslos, the "breast," and eidos, "form," "resem- 
blance."] Shaped like the breast. 

Ma'trix. [Lat.] The womb. Producing or containing substance. 

Max'illary. [From the Lat. maa;i7/a, a " jaw."] Pertaining to the maxillcc 
or jaws. 

Mea'tus. [From the Lat. 7neo, meatum, to "pass."] A passage or 

Medul'la Oblonga'ta. [Lat.] The " oblong marrow " ; that portion of the 
brain which lies within the skull, upon the basilar process of the occip- 
ital bone. 

Meibo'mian. A term applied to the small glands between the conjunctiva 
and tarsal cartilages, discovered by Meibomius. 


Mes'entery. [From the Gr. mesos, "middle," and enteron, the "intestine."] 
A duplicature of the peritoneum covering the small intestine, which 
occupies the middle or centre of abdominal cavity. 

Mes'oblast. [From the Gr. mesos, " middle," and blastos, a " germ " or 
" sprout."] The middle layer of the germinal membrane. 

Mesocolon. A duplicature of the peritoneum covering the colon. 

Metab'olism. [From the Gr. metabole, " change."] The changes taking 
place in cells, whereby they become more complex and contain more 
force, or less complex and contain less force. The former is construc- 
tive metabolism, or anabolism ; the latter, destructive metabolism, or 

Metacar'pus. [From the Gr. meta, " after," and karpos, the " wrist."] The 
part of the hand comprised between the icrist and fingers. 

Metatar'sus. [From the Gr. meta, " after," and tarsos, tlie " instej)."] That 
part of the foot comprised between the instep and toes. 

Metre. [From the Gr. metron, a " measure."] The primary unit of the 
Metric System. The measure of length from which the units of weiglit 
and capacity are derived. It is equivalent to 39.37 inches. A milli- 
metre is one-tliousandth part of a metre. 

Mi'tral. Resembling a mitre. 

Mo'lar. [From the Lat. mola, a "mill."] A term applied to the teeth which 
bruise or grind the food. 

Molec'ular. Pertaining to molecules. 

Mol'ecule. [From the dim. of Lat. moles, a "mass."] The smallest quantity 
into which the mass of any substance can physically be divided. A 
molecule may be chemically separated into two or more atoms. 

Monox'ide. [From the Gr. monos, " single," and " oxide."] A compound 
containing one atom only of oxygen combined with one of base, or 

Mo'tor Oc'uli. [Lat.] INIover of the eye. 

Moto'rial. That which causes movement. 

Mu'cin. The chief constituent of mucus. 

Mu'cous. A term applied to those tissues that secrete mucus. 

Myocar'dium. [From the Gr. mys, niyos, a "muscle," and kardia, the "heart."] 
The muscular structure of the heart. 

Myo'pia. [From the Gr. myo, to " contract," and ops, the " eye."] Near- 

My'osin. Chief proteid substance of muscle. 

Na'ris, pi. Na'res. [Lat.] A nostril. 

Neurilem'ma. [From the Gr. neuron, a " nerve," and lemma, a " coat " or 

" covering."] Xerve-sheath. 
Wi'trogen. A colourless gas forming nearly four-fifths of the atmosphere : the 

diluent of the oxygen in the air. Literally, that which generates nitre. 
Nucle'olus, pi. Nucle'oli. [Dim. of Lat. nucleus, a "kernel."] A smaller 

nucleus witliin the nucleus. 
Nu'cleus, pi. Nu'clei. [Lat. a " kernel."] A minute vesicle embedded in 

the cell protoplasm (cytoplasm). 


Occipi'tal. [From the Lat. occiput, occipitis, the "back of the head."] Per- 
taining to the occiput, the back pai't of the head. 

Odon'toid. [From the Gr. odons, odontos, a " tooth," and eidos, " form," " re- 
semblance."] Tooth-like. 

(Ede'ma. [From the Gr. oideo, to " swell."] A swelling from effusion of 
serous fluid into the areolar tissue. 

(Esoph'agus. [Gr. oisophagos, from oio, (f ut.) oiso, to " carry," and phagema, 
"food."] The gullet. 

Olec'ranon. [From the Gr. olene, the " elbow," and kranon, the " head."] 
The head of the elhow. 

O'lein. [From the Lat. oleum, " oil."] One of the three chief constituents 
of fat. Oil (^oleuin) signifies literally, juice of the olive (l^at. olea). 

Olfac'tory. [From the Lat. olfacio, olfactum, to " smell."] Belonging to the 
sense of smell. 

Omen'tum. [Lat. "entrails."] A duplicature of the peritoneum with more 
or less fat interposed. 

Ophthal'mic. [From the Gr. ophthalmos, the " eye."] Belonging to the eye. 

Op'tic. [From the Gr. opto, to "see."] That which relates to sight. 

O'ra Serra'ta. [Lat.] Serrated border. 

Orbicula'ris. [From dim. of Lat. orhis, an "orb" or "circle."] Name of the 
circular muscles. 

Or'bitaL [From the Lat. orbita, a "track," "rut of a wheel."] Pertaining 
to the 07-bit, the bony cavity in which the eyeball is suspended. 

Os, pi. Ora. [Lat.] A mouth. 

Os, pi. Ossa. [Lat.] A bone. 

Osmo'sis. [From the Gr. usmos, "impulsion."] Diffusion of liquids through 

Os'sa Innomina'ta, pi. of Os Innomina'tum. [Lat.] " Unnamed bones." The 
irregular bones of the pelvis, unnamed on account of their non-resemblance 
to any known object. 

Os'teoblasts. [From the Gr. osteon, a " bone," and blastos, a " germ " or 
"sprout.*'] The germinal cells deposited in the development of Jione. 

O'toliths. [From the Gr. ovs, the "ear," and lithos, a "stone."] Particles 
of calcium carbonate and phosphate found in the internal ear. 

O'vum, pi. O'va. [Lat. an " egg."] The human germ-cell. 

Oxida'tion. The action of oxidizing a body ; that is, combining it with oxy- 
gen, the result of which combination is an oxide. 

Ox'ygen. A tasteless, odourless, colourless gas, forming part of the air, 
water, etc., and supporting life and combustion. 

Pal'mitin. A solid, crystallizable substance of fat, found in the nervous tissue. 

Pal'pebra, pi. Pal'pebrae. [Lat.] The eyelid. 

Pan'creas. A compound secreting gland ; one of the accessory organs of 

nutrition. The sweetbread of animals. 
Papil'lae. [Lat. pi. of papilla, a "nipple," a "pimple."] Minute eminences 

on various surfaces of the body. 
Paraglob'ulin. A. proteid substance of the blood plasma. 
Pari'etaL [From the Lat. paries, parietis, a "wall."] Pertaining to a ivalL 


Parot'id. [From the Gr. para, " near," and ovs, otos, the " ear."] The large 

salivary gland under the ear. 
Parturi'tion. [From the Lat. parturio, 2^a7-turitum, to " bring forth."] The 

act of bringing forth, of giving birth to young. 
Patel'la. [Lat. "a little dish."] A small, io«i'/-shaped bone; the knee-pan. 
Pec'toral. [From the Lat. pectus, pectoris, the "breast."] Pertaining to the 

breast or chest. 
Ped'icle. [From the dim. of Lat. pes, pedis, a " foot."] A stalk. 
Pel' vie. [From the Lat. pelvis, a "basin."] Pertaining to the pelvis, the 

basin or bony cavity forming the lower part of the abdomen. 
Pep'sin. [From the Gr. pepto, to " digest."] A ferment principle in gastric 

juice, having power to convert proteids into peptones. 
Pep'tone. [From the Gr. pepto, to " digest."] A term applied to proteid 

material digested by the action of the digestive juices. 
Pericar'dium. [From the Gr. peri, " about," " around," and kardia, the 

" heart."] The serous membrane covering the heart. 
Perichon'drium. [From the Gr. joen, "about," "around," and chondros, a 

" cartilage."] The serous membrane covering the cartilages. 
Per'ilymph. [From the Gr. peri, "about," "around," and the Lat. hjmpha, 

" water."] The fluid in the osseous, and surrounding the membranous, 

labyrinth of the ear. 
Perios'teum. [From the Gr. peri, "about," "around," and osteon, a "bone."] 

The membrane covering the bones. 
Periph'eral. [From the Gr. peri, " about," " around," and phero, to " bear,"] 

Pertaining to the periphery or circumference ; that which is away from 

the centre and towards the circumference. 
Peristal'sis. [From the Gr. peristello, to " surround," to " compress."] 

Peristaltic action. A term applied to the peculiar movement of the 

intestines, like that of a worm in its progress, by which they gradually 

propel their contents. 
Peritone'um. [From the Gr. periteino, to " stretch around," to " stretch all 

over."] The serous membrane lining the walls and covering the con- 
tents of the abdomen. 
Perone'al. [From the Gtv. perone, the "fibula."] Pertaining to the fbula ; 

a term applied to muscles or vessels in relation to the fbula. 
Pe'trous. [From the Gr. petrd, a "rock."] Having the hardness of rock. 
Pey'er's Glands. The clustered glands in the intestines, so named after the 

anatomist, Peyer, who well described them. 
Phalan'ges. [Lat. pi. of phalanx, a " closely serried array of soldiers."] A 

name given to the small bones forming the fingers and toes, because 

placed alongside one another like a phalanx. 
Phar'ynx. [From the Gr. pharao, to " plough," to " cleave."] The cleft or 

cavity forming the upper part of the gullet. 
Phren'ic. [From the Gr. phren, the " diaphragm."] Pertaining to the dia- 
Pi'a Ma'ter. [Lat. pia (fern.), "tender," "delicate," and mater, "mother."] 

The most internal of the three membranes of the brain. See Dura 



Pig'ment. [From the hat. pigmentum, "paint," "colour."] Colouring matter. 

Pin'na. [Lat. a " feather " or " wing."] External cartilaginous flap of the 

Placen'ta. [Lat. a " thin, flat cake."] A Jlat, circular, vascular substance 
wliich forms the organ of nutrition for the fcetus in utero. 

Plan'tar. [From the Lat. planta, " the sole of the foot."] Pertaining to the 
sole of the foot. 

Plas'ma. [From the Gr., " to form."] A tenacious plastic fluid con- 
taining the coagulating portion of the blood; that in which the blood- 
corpuscles float; the liquor sanguinis. 

Pleu'ra. [Gr. the " side."] A serous membrane divided into two portions, 
lining the right and left cavities of the chest, and reflected over each 

Plex'us. [From the Lat. plecto, plexum, to " knit " or " weave."] A netivork 
of nerves or veins. 

Pneumogas'tric. [From the Gr. pneumun, a "lung," and gaster, the "stom- 
ach."] Pertaining to the hnigs and stomach. 

Polyhe'dral. [From the Gr. puhjs, " many," and hedra, a " base," a " side."] 

Pons Varo'lii. [Lat.] " Bridge of Varolius." The white fibres which form 
a bridge connecting the different parts of the brain, first described by 

Poplite'al. [From the Lat. poples, poplitis, the " ham," the " back part of the 
knee."] The space behind the knee-joint is called the popliteal space. 

Prismat'ic. Resembling a prism, which, in optics, is a solid, glass, triangular- 
shaped body. 

Prona'tion. [From the l^at. pronus, "inclined forwards."] The turning of 
the hand with the jialm forwards. 

Prona'tor. The group of muscles which turn the hand palm forwards. 

Pro'teids. A general term for the albuminoid constituents of the body. 

Pro'toplasm. [From the Gr. protos, "first," a.ud plasso, to "form."] AJirst- 
f armed organized substance ; primitive organic cell matter. 

Pseudostom'ata. [From the Gr. j^seudes, " false," and stoma, stomatos, a 
" mouth."] False openings. 

Pter'ygoid. [From the Gr. j)teron, a "wing," and eidos, "form," " resem- 
bhuice."] Wing-like. 

Pty'alin. [From the Gr. ptyalon, "saliva."] A ferment principle in saliva, 
having power to convert starch into sugar. 

Pu'bes, gen. Pu'bis. [Lat.] The external part of the generative region ; 
the portion of the os innominatum forming the front of the pelvis. 

Pul'monary. [From the Lat. puhno, Tpil. pulmones, the "lungs."] Relating 
to the lungs. 

Pylor'ic. Pertaining to the pylorus. 

Pylor'us. [From the Gr. pi/le, a " gate " or " entrance," and owos, a 
"guard."] The lower orifice of the stomach, furnished with a circular 
valve which closes during stomach digestion. 
Pyrex'ia. [From the Gr. pj/resso, (fut.) pip-exo, to "have a fever."] Eleva- 
tion of temjierature ; fever. 


Quad'riceps. [From the Lat. (jualuor, " four," and caput, the " head."] A 
term applied to the extensor muscle of the leg, having four heads or 

Ra'dius. [Lat. a " rod," the " spoke of a wheel."] The outer bone of the 

fore-arm, so called from its shape. 
Rale. [From the Fr. rdler, to "rattle in the throat."] A rattling, bubbling 

sound attending the circulation of air in the lungs. Different from the 

murmur produced in health. 
Rec'tus. [Lat.] Straight. 

Re'nal. [From the Lat. ren, rents, the " kidneys."] Pertaining to the kid- 
Ren'nin. (Rennet.) The milk curdling enzyme which constitutes the active 

principle of rennet. 
Retic'ular. [From the Lat. reticulum, a "small net."] Resembling a small 

Ret'iform. [From the Lat. rete, a " net," and forma, " form."] Having the 

form or structure of a net. 
Ret'ina. [From the Lat. rete, a " net."] The most internal membrane of 

the eye ; the expansion of the optic nerve. 
Ri'ma Glot'tidis. [Lat. rima, a "chink" or "cleft."] The opening of the 

Ru'gSB. [Lat. pi. of ruga, a "wrinkle."] A term applied to the folds or 

wrinkles in the mucous membrane, especially of the stomach and vagina. 

Sa'crum. [Lat. neut. of sacer, " sacred."] The large triangular bone above 
the coccyx, so named because it was supposed to protect the organs con- 
tained in the pelvis, which were offered in sacrifice and considered 

Sag'ittal. [From the Lat. sagitta, an " arrow."] Arrow-shaped. 

Sal'ivary. Pertaining to the saliva, the fluid secreted by the glands of the 

Saphe'nous. [From the Gr. sapJics, " manifest."] A name given to the two 
large superficial veins of the lower limKs. 

Saponifica'tion. [From the Lat. sapo, saponis, "soap," and facio, to "make."] 
Conversion into soap. 

Sarcolem'ma. [From the Gr. sa7-x, sarkos, "flesh," and lemma, a "cover- 
ing."] The covering of the individual muscle fibrils. 

Sar'cous. [From the Gr. sarx, sarkos, "flesh."] Fleshy, belonging to fesh. 

Sarto'rius. [From the Lat. sartor, a " tailor."] The name of the muscle 
used in crossing the legs, as a tailor does when he sits and sews. 

Scap'ula. [Lat.] The shoulder-blade. 

Sclerot'ic. [Lat. scleroticus, from Gr. skleroo, to " harden."] Hard, tough. 

Seba'ceous. A term applied to glands secreting sebum. 

Se'bum or Se'vum. [Lat. sevum, "suet."] A fatty secretion resembling 
suet, which lubricates the surface of tlie skin. 

Semilu'nar. [From the Lat. semis, " half," and luna, the " moon."] Having 
the shape of a halfynoon. 


Se'rous. Having the nature of serum. 

Se'rum. [Lat.] The watery fluid separated from the blood after coagula- 
Ses'amoid. [From the Gr. sesamon, a "seed of the sesamuni," and eidos, 
"form," "resemblance."] Resembling a grain of sesamum. A term 
applied to the small bones situate in the substance of tendons, near 
certain joints. 
Sig'moid. From the Gr. letter 5, sigma, and eidos, " form," " resemblance."] 

Curved like the letter S. 
Sole'us. [From the Lat. solea, a "sandal."] A name given to a muscle 

shaped like the sole of a shoe. 
Specific Grav'ity. The comparative density or gravity of one body con- 
sidered in relation to another assumed as the standard. In measuring 
the specific gravity of liquids or solids, water is usually taken as the 
standard of comparison, being reckoned as a unit. 
Sphe'noid. [From the Gr. sphen, a "wedge," and eidos, "form," "resem- 
blance."] Like a wedge. 
Sphinc'ter. [From the Gr. sphiggo, to "bind tight," to "close."] A circu- 
lar muscle which contracts the aperture to which it is attached. 
Squa'mous. [From the Lat. squama, a " scale."] Scale-Wke. 
Sta'sis. [From the Gr. stao, to " stop."] Stagnation of the blood current. 
Ste'arin. One of the three chief constituents of fat. 
Ster'num. [Lat.] The breast-bone. 

Stim'ulus, pi. Stim'uli. [Lat. a "goad."] Anything that excites to action. 
Sto'ma, pi. Stom'ata. [From the Gr. stoma, stomatos, a " mouth."] A 

mouth; a small opening. 
Strat'ified. [From the Lat. stratum, a " layer," and facio, to " make."] 

Formed or composed of strata or layers. 
Stri'ated. [From the Lat. strio, striatum, to "make furrows."] That which 

has strice, furrows or lines. 
Stro'ma. [From the Gr. stroma, a " bed."] The foundation or hed tissue of 

an organ. 
Styloglos'sus. [From the Gr. stylos, a " pillar," and glussa, the " tongue."] 
A muscle connected with a, pointed style-like process of the temporal bone 
and the tongue. 
Subcla'vian. Under the clavicle. 
Subcuta'neous. [From the Lat. sub, "under," and cutis, the "skin."] Under 

the skin. 
Sudoriferous. [From the Lat. sudor, " sweat," and fero, to " carry," to 

" bear."] A term applied to the glands secreting sweat. 
Supina'tion. [From the Lat. supino, supinatum, to "bend backwards," to 
" place on the back."] The turning of the hand with the palm back- 
wards, the posterior surface of the hand being supine. 
Su'pinators. The muscles which turn the hand with the palm backwards. 
Suprare'nal. [From the Lat. sw^cr, "over," and ren, renis, the "kidney."] 

Above the kidney. 
Su'ture. [From the Lat. suo, sutum, to "sew together."] That which is 
sewn together, a seam; the seam uniting bones of the skull. 


Sym'physis. [From the Gr. syn, "together," and phyo, to "produce," to 

"grow."] A union of bones, usually of symmetrical bones in the 

median line, as the pubic bones and bones of the jaw. 
Synarthro'sis. [From the Gr. syn, "together," and arthron, a "joint."] A 

form of articulation in which the bones are immovably joined together. 
Synchondro'sis. [From the Gr. syn, " together," and chondros, " cartilage."] 

Union by an intervening growth of cartilage. 
Syndosmo'sis. [From the G\\ syn, "together," and desmos, a "ligament."] 

Union by ligaments. 
Syno'via. [Supposed to be from the Gr. syn, " together," implying union 

or close resemblance, and oon, an " Qg%"'\ A fluid resembling the white 

of an egg. 
Syno'vial. Pertaining to synovia. 
Syn'tonin. [From the Gr. synteino, to "stretch," to "draw," referring to 

the peculiar property of muscular fibre.] A name given by Lehmann 

to a substance obtained from muscular fibre by the action of dilute 

muriatic acid. 
Sys'tole. [From the Gr. systello, to " draw together," to " contract."] The 

contraction of the heart. 

Tar'sus. [From the Gr. tarsos, the " instep."] The instep : the cartilage of 
the eyelid. 

Ten'do Achil'lis. [Lat.] "Tendon of Achilles." The tendon attached to 
the heel, so named because Achilles is supposed to have been held by the 
heel when his mother dipped him in the river Styx to render him invul- 

Thorac'ic. [From the Gr. thorax, a " breastplate," the " breast."] Pertain- 
ing to the thorax. 

Thy'roid. [From the Gr. thyreos, an "oblong shield," and eidos, "form," 
" resemblance."] Resembling a shield. A name given to an opening in 
the ossa innominata : to the piece of cartilage forming the anterior 
prominence of the larynx : to the gland placed in front of the larynx. 

Tib'ia. [Lat. a "flute" or "pipe."] The shin-bone, called tibia, from its 
fancied resemblance to a reed-pipe. 

Tibia'lis Anti'cus. [Lat.] The muscle situate at the anterior part of the 

Tibia'lis Pos'ticus. [Lat.] The muscle situate at the posterior part of the 

Tone. [Gr. tonos, from teino, to " stretch."] A distinct sound. The state 
of tension proper to each tissue. A term used to express the normal 
excitability, strength, and activity of the various organs and functions 
of the body in a state of health. 

Trabec'ulae. [Lat. pi. of trabecula, a "little beam."] A term applied to 
prolongations of fibrous membranes which form septa, or partitions. 

Tra'chea. [Lat.] The windpipe. 

Transversa'lis. [Lat. from trans, "across," and verto, versum, to "turn," to 
" direct."] A term applied to a muscle which runs in a transverse direc- 


Trape'zius. A name given to the two upper superficial muscles of the back, 

because together they resemble a trapezium, or diamond-shaped quad- 
Tri'ceps. [From the Lat. tres, " three," and caput, the " head."] A term 

applied to a muscle having a triple origin, or three heads. 
Tri'cuspid. [From the Lat. tres, "three," and cuspis, cuspidis, a "point."] 

Having three points. 
Trochan'ter. [From the Gr. trochao, to " turn," to " revolve."] Name given 

to two projections on the upper extremities of the femur, which give 

attachment to the rotator muscles of the thigh. 
Tryp'sin. The ferment principle in pancreatic juice which converts proteid 

material into peptones. 
Tuberos'ity. [From the Lat. tuber, tuheris, a, "swelling."] A protuberance. 
Tur'binated. [Lat. turbinatus, from turbo, tm-binis, a " top."] Formed like 

a top; a name given to the bones in the outer wall of the nasal 

Tym'panum. [From the Gr. tympanon, a " drum."] The drum or hollow 

part of the middle ear. 

Ul'na. [Lat. the "elbow."] The inner bone of the fore-arm, the olecranon 

process of which forms the elbow. 
Umbil'icus. [Lat. the "navel."] Around cicatrix or scar in the median 

line of the abdomen. 
TJ'rea. [From the Lat. urina, "urine."] Chief solid constituent of urine. 

Nitrogenous product of tissue decomposition. 
Ure'ter. [From the Gr. oureu, to " pass urine."] The tube through which 

the urine is conveyed from the kidney to the bladder. 
Ureth'ra. [From the Gr. owed, to " pass urine."] The canal throiigh which 

the urine is conveyed from the bladder to the meatus urinarius. 
U'vula. [Dim. of Lat. uva, a "grape."] The small, elongated, fleshy body 

hanging from the soft palate. 

Vag'inaL [From the Lat. vagina, a " sheath."] Sheath-Vike. 

Val'vulae Conniven'tes. [Lat.] A name given to transverse folds of the 
mucous membrane in the small intestine. 

Vas'a Vaso'rum. [Lat.] " The vessels of the vessels." The small blood- 
vessels which supply the walls of the larger hlood-vessels with blood. 

Vas'cular. [From the Lat. vasculum, a "little vessel."] Relating to vessels; 
full of vessels. 

Va'so-constric'tor. [From the Lat. vas, a " vessel," and constrincjuo, to " con- 
strict."] An agent which brings about con:<triction of blood-i'e.s\se/.v ; spe- 
citically a nerve when stimulated, or a drug which acts in this way when 

Va'so-dila'tor. [From the Lat. vas, a " vessel," and dilator, a " dilator."] 
An agent which brings about dilatation of h\ood-vessels. 

Ve'nae Ca'vae, pi. of Ve'na Ca'va. [Lat.] " Hollow veins." A name given 
to the two great veins of the body which meet at the right auricle of the 


Ve'nae Com'ites. [Lat.] " Attendant veins." Veins which accompany the 

Ven'tral. [From the Lat. venter, ventris, the "belly."] Belonging to the 
belly cavity. 

Ven'tricle. [From the dim. of Lat. venter, the "belly."] A small cavity. 

Ver'miform. [From the Lat. vermis, a "worm," and forma, "form."] Worm- 

Ver'nix Caseo'sa. [Lat.] "Cheesy varnish." The fatty varnish found on 
the new-born infant, which is secreted by the sebaceous glands of the 

Ver'tebrae, pi. of Ver'tebra. [Lat. from verto, to " turn."] The bones of the 

Vil'li. [Lat. pi. of villus, "shaggy hair."] The conical projections on the 
valvulte conniventes, making the mucous membrane look shaggy. 

Vis'cera. [Lat.] The internal organs of the body. 

Vitel'line. [From the Lat. vitellus, the "yolk of an egg."] A term applied 
to the yolk membrane. 

Vitel'lus. [Lat. from vita, " life."] The yolk of an egg. 

Vit'reous. [From the Lat. vitrum, " glass."] G^Zass-like. A name applied to 
the transparent, jelly-like substance which fills the back part of the eye- 
ball behind the crystalline lens. 

Vo'mer. [Lat. a "ploughshare."] The thin plate of bone shaped some- 
what like & ploughshare which separates the nostrils. 

Vul'va. The external female genitals. 

Zo'na Pellu'cida. [Lat.] " Pellucid zone." The broad, transparent ring 
which surrounds the yolk in the centre of the ovum. 



Abdomen, divisions of, 176. 

Absorption, 197. 

Adipose tissue, 17. 

Adjustment of eye, how accomplished, 239. 

Air, composition of, 160. 

Albumin, 100. 

Alimentary canal, 175. 

Alimentation, 164. 

Amoeboid movement, 5, 99. 

Aorta, 116. 

Aponeuroses, 16, 62. 

Arachnoid membrane, 85. 

Arterial distribution, plan of, 129; some 
features of, 131. 

Arterial tension, 133. 

Arteries, of head and neck, 118; of lower 
limb, 123; structure of. 111; table of, 
129; of upper limb, 119. 

Artery, innominate, 116; pulmonary, 128. 

Articulations, freely movable, 49; im- 
movable, 48 ; slightly movable, 48. 

Atoms, 3. 

Auditory canal, 228. 

Axones, 74. 


Bile, 188, 194. 

Bladder, 204. 

Blood, the, 96; circulation of, 131; clot- 
ting of, 100 ; functions of, 95, 102 ; gen- 
eral composition of, 101 ; red corpuscles 
of, 96 ; white corpuscles of, 98. 

Blood-vessels, 95. 

Body, chemical composition of, 172. 

Bone, description of, 20; development of, 
22 ; regeneration of, 22. 

Bones, of cranium, 33; of face, 37; flat, 
25 ; irregular, 25 ; long, 24 : of lower ex- 
tremity, 28; short, 25; table of, 47; of 
upper extremity, 25. 

Brain, description of, 85. 

Bread, composition of, 173. 

Bursae, 51. 


Cajcum, 184. 

Canal, alimentary, 175; auditory, 228; 
central, of spinal cord, 81. 

Canals, Haversian, 21. 

Capillaries, 113. 

Carbo-hydrates, 170. 

Carbonic dioxide, excretion of, 161; pro- 
portion of, in air, 160. 

Cavity, buccal, 177; dorsal, 2; pelvic, 45; 
thoracic, 42; ventral, 2. 

Cell, the, 3. 

Cerebellum, 86, 94. 

Cerebrum, 87, 94. 

Chordae tendinse, 107. 

Choroid of the eye, 235. 

Chyle, 144. 

Cilia, 11. 

Circulation, arterial, 131; capillary, 134; 
fffital, 1.37; general, 131; portal, 125; 
pulmonary, 131 ; summary of, 137. 

Coccyx, 41. 

Colon, 184. 

Conjunctiva, 240. 

Connective tissue proper, 14, 

Connective tissues, classification of, 13. 

Contractility, muscular, 53, 54. 

Cord, spinal, 80. 

Corpuscles, tactile, 214, 223; red, 96; 
white, 98. 

Cranial nerves, 88. 

Cranium, 43. 

Crystalline lens, 238. 

Cutis vera, 213. 

Cytoplasm, 3, 74. 


Dendrones, 74. 

Development of blood-vessels and cor- 
puscles, 140 ; bone, 22 ; muscular tissue^ 

Diaphragm, 66. 

Diastole, 109. 

Diet, 174. 




Digestion, 191. 

Digestive juices, bile, 194; gastric, 193; 

intestinal, 195; pancreatic, 195; saliva, 

Diploe, 25. 
Duct, cystic, 190; hepatic, 189; nasal, 242; 

pancreatic, 185; right lymphatic, 143; 

thoracic, 143. 
Dura mater, 85. 


Ear, the, 228. 

Elastic tissue, 16. 

Elimination, 202. 

Endothelium, 111. 

Enzyme, 191. 

Epidermis, 213. 

Epithelium, 9. 

Equilibrium, sense of, 232. 

Eustachian tube, 180, 229. 

Eye, the, 233; choroid coat of, 235; crys- 
talline lens of, 238; sclerotic coat of, 
233 ; refracting media of, 237 ; retina of, 

Eyebrows, 240. 

Eyelids, 240. 


Fallopian tubes, 243, 247. 

FasciiB, 10, 71. 

Fats, 170 ; absorption of, 198 ; digestion of, 

Feces, 19<;. 

Fibres, non-striated muscular, 54; stri- 
ated muscular, 53. 

Fibrin, 100. 

Fibrinogen, 100. 

Fibro-cartilage, 18. 

Fibrous tissue, 15. 

Foetal circulation, 137. 

Fontanelles, 44. 

Food, 1(59. 

Food-stuffs, classification of, 169. 

Foramen, thyroid, 30; magnum, 33, 


Gall-bladder, 190. 

Ganglia, 77; sympathetic, 78, 92 ; spinal, 
83, 92. 

Gastric juices 193. 

Glands, lachrymal, 241; lymphatic, 146; 
mammary, 2.50; Meibomian, 241; sali- 
vary, 178; sebaceous, 216; secreting, 
164; solitary, 148; sweat, 217. 

Glottis, 1,52. 

Glycogen, 198. 

Gullet, 180. 


Hfenioglobin, 97. 
Hairs, the, 215. 

Hearing, sense of, 231. 

Heart, beat of the, 108; cavities of the, 
10(j; description of the, 103; sounds of 
the, 110. 

Heat, bodily, 219; distribution of, 220; 
loss of, 219 ; production of, 219 ; regula- 
tion of, 220. 

Humours of the eye, 237. 

Ileo-crecal valve, 184. 
Inliammation, 136. 
Insensible perspiration, 218. 
Intestinal juice, 195. 
Intestine, large, 184; small, 182. 
Iris, 235. 

Joints, classification of, 42 ; movements 
of, 49, 50, 51 ; table of, 52. 

Juice, gastric, 193; intestinal, 195; pan- 
creatic, 195. 


Kidneys, blood-supply of, 206; position 
of, 203 ; structure of, 205. 

Labyrinth of ear, 230. 

Lachrymal glands, 241. 

Lacteals, 183, 198. 

Larynx, 151. 

Ligament, Poupart's, 64. 

Ligamenta subflava, 16. 

Ligaments, 15, 49; annular, 71; broad, 
246; round, 246. 

Light, 240. 

Linea alba, 64. 

Liver, the, 186. 

Lungs, 155, 157. 

Lymph, 143; functions of, 145; move- 
ments of, 144. 

Lymphatic glands, 146 ; vessels, 142. 

Lymphatics, 141. 


Mammary glands, 250. 

Marrow, 220. 

^Mastication, 192. 

ISIeat, composition of, 173. 

Medulla oblongata, 85, 92. 

Mcdullated nerve fibres, 76. 

Meibomian glands, 241. 

Membranes, mucous, 166; serous, 113; 

synovial. 49, 51. 
Metabolism, 4, 201. 
Milk, composition of, 173, 251. 
Mineral salts, 100, 171. 



Molecules, 3. 

Mouth, the, 177. 

Muscles, action of abdominal, 64; attach- 
ment of, 5(j ; of head and face, 58 ; of lower 
extremity, G9 ; of neck and trunk, 61 ; 
relation of nerves to, 71; table of, 72; 
of upper extremity, 67. 

Muscular tissue, description of, 53; de- 
velopment of, 56 ; regeneration of, 56. 


Nails, the, 215. 

Nares, anterior, 226 ; posterior, 227. 

Nerves, afferent or sensory, 77 ; cranial, 88 
degeneration and regeneration of, 84 
description of, 76 ; efferent or motor, 77 
spinal, 82; vaso-motor, 79. 

Nervous system, divisions of, 75; physiol- 
ogy of, iX). 

Neurone, the, 74. 

Nitrogenous waste, excretion of, 210. 

Nose, the, 226. 

Nucleus of cell, 3, 5. 


OEdema, 145. 
(Esophagus, 150. 
Ovaries, 247. 
Ovum, 249. 
Oxidation, 98, 161. 

Oxygen, combination of, with haemo- 
globin, 98, 161. 

Plasma of the blood, 102. 

Pleura, 114, 157. 

Pons Varolii, 86, 92. 

Pressure, atmospheric, 157; sense, 223. 

Process, acromion, 26; alveolar, 38; an- 
terior superior spinous, of ilium, 30; 
odontoid, 40; olecranon, 27. 

Processes of bone, 25. 

Proteids, 169. 

Protoplasm, 4. 

Ptyalin, 192. 

Pulse, the, 1.32. 

Pylorus of stomach, ^81. 

Pyramids of kidney, 205. 

Pyrexia, 220. 


Receptacle of chyle, 143. 

Rectum, 185. 

Reflex action, 90. 

Rennin, 193. 

Respiration, 66, 151, 157; costal, 66; 
diaphragmatic, 66; effect of, upon air 
outside body, 159; effect of, upon air 
within lungs, 158 ; effect of, upon blood, 

Respiratory movements, modified, 162. 

Retina, 235. 
Ribs, 43. 


Sacrum, 40. 
Saliva, 192. 
Salivary glands, 178. 
Scarpa's triangle, 124. 
Sebaceous glands, 178. 
Secreting glands, 164. 
Secretion, 194. 
Sensation, common, 224. 
Serous membranes, 113. 
Sight, long and near, 239; sense of, 233. 
Skeleton, the, 24. 
Skin, the, 212. 
Skull, 43. 

Smell, sense of, 226. 
Sound, 231. 
Special senses, 222. 

Sphincter muscle of bladder, 204; of rec- 
tum, 185. 
Spinal cord, 80, 92; nerves, 82. 
Spiue, the, 39, 41. 
Spleen, the, 149. 
Stomach, 180. 

Subnormal temperature, 221. 
Succus entericus, 195. 
Supra-renal capsules, 210. 
Sutures, 48, 52. 
Sweat-glands, 217. 
Symphysis pubis, 30. 
Synovia, 51. 

System, sympathetic, 78. 
Systole, 109. 

Taste, sense of, 224. 

Tears, 241. 

Teeth, 178. 

Temperature, blood, 96; of body, 219; 
sense of, 224; subnormal, 221. 

Tendons, 16. 

Tension, arterial, 133. 

Thorax, 42. 

Tissue, adipose, 17; areolar, 14; carti- 
laginous, 18; connective, proper, 14; 
elastic, 16; epithelial, 8; fibrous, 15; 
muscular, 53; nervous, 74; osseous, 20. 

Tissues, classification of, 7. 

Tongue, the, 178, 224. 

Tonsils, 149. 

Touch, sense of, 223. 

Trachea, 153. 

Tube, Eustachian, 180, 229 ; Fallopian, 243, 

Tympanum, 229. 

Urea, 209. 
Ureters, 203. 
Urethra, 204. 




Urine, composition of, 209; excretion of , 
208 ; secretion of, 207. 

Uterus, 243. 

Uvula, 177. 


Vagina, 243. 

Valves of heart, 106 ; in veins, 112. 

Valvulse conniventes, 182. 

Vascular system, 95. 

Vein, portal, 125. 

Veins, of head and neck, 126; of lower 
limb, 127; pulmonary, 128; right and 
left azygos, 127; structure of, 112; sys- 
temic veins, 125 ; table of, 129 ; of upper 
limb, 126. 

VeuEB comites, 125. 

Ventricles of the brain, 86; of the heart, 

106, 107. 
Vermiform appendix, 184. 
Vertebrae, description of, 39, 40. 
Villi, 168. 
Vocal cords, 152. 


Waste products, 202. 
Water, composition of, 171. 


Zona pellucida, 249. 

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University of